diff --git a/frontend/templates/file_detail.html b/frontend/templates/file_detail.html
index f329b6c2..4681086f 100644
--- a/frontend/templates/file_detail.html
+++ b/frontend/templates/file_detail.html
@@ -1528,11 +1528,11 @@
   {% endif %}
 
   <!-- File Preview Card -->
-  {% if file_exists or processed_exists %}
+  {% if original_file_exists or processed_file_exists %}
   <div class="detail-card">
     <h3>File Previews</h3>
     <div style="display: grid; grid-template-columns: repeat(auto-fit, minmax(400px, 1fr)); gap: 2rem;">
-      {% if file_exists %}
+      {% if original_file_exists %}
       <div>
         <h4 style="font-weight: 600; color: #2d3748; margin-bottom: 1rem;">Original File</h4>
         <div style="border: 2px solid #e2e8f0; border-radius: 0.5rem; overflow: hidden; background-color: #f7fafc;">
@@ -1541,36 +1541,46 @@
           <img src="/api/files/{{ file.id }}/preview?version=original" alt="{{ file.original_filename }}" style="width: 100%; height: auto; display: block;">
           {% elif file.mime_type and file.mime_type.startswith('text/') %}
           <!-- Text file preview -->
-          <iframe src="/api/files/{{ file.id }}/preview?version=original" style="width: 100%; height: 600px; border: none;"></iframe>
+          <iframe src="/api/files/{{ file.id }}/preview?version=original" title="Original text file preview" style="width: 100%; height: 600px; border: none;"></iframe>
           {% else %}
-          <!-- PDF and other documents -->
-          <iframe src="/api/files/{{ file.id }}/preview?version=original" style="width: 100%; height: 600px; border: none;"></iframe>
+          <!-- PDF via pdf.js (rendered by loadPDF above) — fallback canvas container -->
+          <div id="detail-original-canvas" class="pdf-canvas-wrapper" style="min-height: 400px; display: flex; justify-content: center; align-items: center; padding: 0.5rem;">
+            <div class="pdf-loading">
+              <i class="fas fa-spinner fa-spin" aria-hidden="true" style="font-size: 2rem; margin-bottom: 1rem;"></i>
+              <p>See PDF viewer above</p>
+            </div>
+          </div>
           {% endif %}
         </div>
         <div style="margin-top: 0.5rem; text-align: center; display: flex; gap: 1rem; justify-content: center;">
           <a href="/api/files/{{ file.id }}/preview?version=original" target="_blank" style="color: #3182ce; text-decoration: none; font-size: 0.875rem;">
-            <i class="fas fa-external-link-alt"></i> Open in new tab
+            <i class="fas fa-external-link-alt" aria-hidden="true"></i> Open in new tab
           </a>
           <a href="/api/files/{{ file.id }}/download?version=original" style="color: #3182ce; text-decoration: none; font-size: 0.875rem;">
-            <i class="fas fa-download"></i> Download
+            <i class="fas fa-download" aria-hidden="true"></i> Download
           </a>
         </div>
       </div>
       {% endif %}
 
-      {% if processed_exists %}
+      {% if processed_file_exists %}
       <div>
         <h4 style="font-weight: 600; color: #2d3748; margin-bottom: 1rem;">Processed File</h4>
         <div style="border: 2px solid #e2e8f0; border-radius: 0.5rem; overflow: hidden; background-color: #f7fafc;">
-          <!-- Processed files are typically PDFs -->
-          <iframe src="/api/files/{{ file.id }}/preview?version=processed" style="width: 100%; height: 600px; border: none;"></iframe>
+          <!-- Processed files are typically PDFs — rendered by pdf.js above -->
+          <div style="min-height: 400px; display: flex; justify-content: center; align-items: center; padding: 0.5rem;">
+            <div class="pdf-loading">
+              <i class="fas fa-spinner fa-spin" aria-hidden="true" style="font-size: 2rem; margin-bottom: 1rem;"></i>
+              <p>See PDF viewer above</p>
+            </div>
+          </div>
         </div>
         <div style="margin-top: 0.5rem; text-align: center; display: flex; gap: 1rem; justify-content: center;">
           <a href="/api/files/{{ file.id }}/preview?version=processed" target="_blank" style="color: #3182ce; text-decoration: none; font-size: 0.875rem;">
-            <i class="fas fa-external-link-alt"></i> Open in new tab
+            <i class="fas fa-external-link-alt" aria-hidden="true"></i> Open in new tab
           </a>
           <a href="/api/files/{{ file.id }}/download?version=processed" style="color: #3182ce; text-decoration: none; font-size: 0.875rem;">
-            <i class="fas fa-download"></i> Download
+            <i class="fas fa-download" aria-hidden="true"></i> Download
           </a>
         </div>
       </div>
diff --git a/frontend/templates/file_view.html b/frontend/templates/file_view.html
index 0aaa77fd..ac0548e1 100644
--- a/frontend/templates/file_view.html
+++ b/frontend/templates/file_view.html
@@ -3,6 +3,11 @@
 
 {% block head_extra %}
   <script src="/static/js/common.js"></script>
+  <!-- PDF.js library (Apache 2.0 License - compatible) -->
+  <script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.min.js"></script>
+  <script>
+    pdfjsLib.GlobalWorkerOptions.workerSrc = 'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js';
+  </script>
   <style>
     .doc-container { max-width: 1200px; margin: 0 auto; }
 
@@ -51,7 +56,61 @@
     /* ── tags ── */
     .tag-pill { display: inline-block; padding: 0.15rem 0.6rem; border-radius: 9999px; font-size: 0.75rem; font-weight: 500; background: #f0fdf4; color: #15803d; margin: 0.1rem; }
 
-    /* ── preview iframe ── */
+    /* ── pdf.js viewer ── */
+    .pdf-viewer { position: relative; background: #525659; border-radius: 0.375rem; overflow: hidden; }
+    .pdf-controls {
+      display: flex; align-items: center; justify-content: center; gap: 0.75rem;
+      padding: 0.5rem; background: #f1f5f9; border-radius: 0.375rem 0.375rem 0 0;
+    }
+    .pdf-nav-btn {
+      padding: 0.35rem 0.75rem; border: 1px solid #cbd5e1; border-radius: 0.25rem;
+      background: white; color: #374151; font-size: 0.8rem; cursor: pointer;
+      min-height: 36px; min-width: 36px;
+    }
+    .pdf-nav-btn:disabled { opacity: 0.4; cursor: default; }
+    .pdf-nav-btn:hover:not(:disabled) { background: #e2e8f0; }
+    .pdf-page-info { font-size: 0.8rem; color: #374151; font-weight: 600; min-width: 100px; text-align: center; }
+    .pdf-canvas-wrap { display: flex; justify-content: center; padding: 0.75rem; min-height: 400px; max-height: 700px; overflow: auto; }
+    .pdf-canvas-wrap canvas { max-width: 100%; height: auto; }
+
+    /* ── image viewer with zoom/pan ── */
+    .img-viewer { position: relative; background: #f1f5f9; border-radius: 0.375rem; overflow: hidden; }
+    .img-controls {
+      display: flex; align-items: center; justify-content: center; gap: 0.5rem;
+      padding: 0.5rem; background: #f1f5f9; border-radius: 0.375rem 0.375rem 0 0;
+    }
+    .img-controls button {
+      padding: 0.35rem 0.6rem; border: 1px solid #cbd5e1; border-radius: 0.25rem;
+      background: white; color: #374151; font-size: 0.85rem; cursor: pointer;
+      min-height: 36px; min-width: 36px;
+    }
+    .img-controls button:hover { background: #e2e8f0; }
+    .img-wrap {
+      display: flex; justify-content: center; align-items: center;
+      overflow: auto; max-height: 650px; min-height: 300px; cursor: grab;
+      padding: 0.5rem; background: #525659;
+    }
+    .img-wrap.dragging { cursor: grabbing; }
+    .img-wrap img { transition: transform 0.15s ease; transform-origin: center center; }
+
+    /* ── text viewer ── */
+    .text-viewer { border-radius: 0.375rem; overflow: hidden; }
+    .text-viewer-header {
+      display: flex; align-items: center; justify-content: space-between;
+      padding: 0.5rem 0.75rem; background: #f1f5f9; border-radius: 0.375rem 0.375rem 0 0;
+    }
+    .text-viewer-header span { font-size: 0.8rem; color: #374151; font-weight: 600; }
+    .text-content {
+      background: #1e293b; color: #e2e8f0; padding: 1rem; font-family: 'SFMono-Regular', Consolas, monospace;
+      font-size: 0.82rem; line-height: 1.65; max-height: 600px; overflow: auto; white-space: pre-wrap; word-break: break-word;
+      tab-size: 4;
+    }
+    .text-content .line-number {
+      display: inline-block; width: 3.5em; color: #64748b; text-align: right;
+      margin-right: 1em; user-select: none; font-size: 0.75rem;
+    }
+
+    /* ── preview iframe fallback ── */
     .preview-frame { width: 100%; height: 600px; border: none; border-radius: 0.375rem; background: #f1f5f9; display: block; }
 
     /* ── text box ── */
@@ -271,27 +330,75 @@
       </div>
     </div>
 
-    <!-- RIGHT: PDF preview -->
+    <!-- RIGHT: Document preview -->
     <div>
       <div class="doc-card" style="padding:1rem;">
+        {% set preview_mime = file.mime_type or 'application/pdf' %}
+        {% set preview_version = 'processed' if processed_file_exists else 'original' %}
+        {% set has_preview = processed_file_exists or original_file_exists %}
+
+        {% if preview_mime.startswith('image/') %}
+        <div class="doc-card-title"><i class="fas fa-image" aria-hidden="true" style="color:#8b5cf6;margin-right:0.4rem;"></i>Preview</div>
+        {% elif preview_mime.startswith('text/') %}
+        <div class="doc-card-title"><i class="fas fa-file-code" aria-hidden="true" style="color:#059669;margin-right:0.4rem;"></i>Preview</div>
+        {% else %}
         <div class="doc-card-title"><i class="fas fa-file-pdf" aria-hidden="true" style="color:#ef4444;margin-right:0.4rem;"></i>Preview</div>
-        {% if processed_file_exists %}
-          <iframe
-            src="/api/files/{{ file.id }}/preview?version=processed"
-            class="preview-frame"
-            title="Processed document preview">
-          </iframe>
-          <div style="font-size:0.75rem;color:#9ca3af;margin-top:0.4rem;text-align:right;">Processed version</div>
-        {% elif original_file_exists %}
-          <iframe
-            src="/api/files/{{ file.id }}/preview?version=original"
-            class="preview-frame"
-            title="Original document preview">
-          </iframe>
-          <div style="font-size:0.75rem;color:#9ca3af;margin-top:0.4rem;text-align:right;">Original version</div>
+        {% endif %}
+
+        {% if has_preview %}
+          {% if preview_mime.startswith('image/') %}
+          <!-- ── Image viewer with zoom / pan ── -->
+          <div class="img-viewer" id="img-viewer">
+            <div class="img-controls">
+              <button onclick="imgZoom(1.25)" title="Zoom in" aria-label="Zoom in"><i class="fas fa-search-plus" aria-hidden="true"></i></button>
+              <button onclick="imgZoom(0.8)" title="Zoom out" aria-label="Zoom out"><i class="fas fa-search-minus" aria-hidden="true"></i></button>
+              <button onclick="imgReset()" title="Reset zoom" aria-label="Reset zoom"><i class="fas fa-expand" aria-hidden="true"></i></button>
+              <span id="img-zoom-level" style="font-size:0.8rem;color:#6b7280;min-width:3em;text-align:center;">100%</span>
+            </div>
+            <div class="img-wrap" id="img-wrap">
+              <img
+                id="preview-img"
+                src="/api/files/{{ file.id }}/preview?version={{ preview_version }}"
+                alt="{{ file.original_filename }}"
+                draggable="false"
+                style="max-width:100%;height:auto;">
+            </div>
+          </div>
+
+          {% elif preview_mime.startswith('text/') %}
+          <!-- ── Text file viewer with line numbers ── -->
+          <div class="text-viewer" id="text-viewer">
+            <div class="text-viewer-header">
+              <span><i class="fas fa-file-code" aria-hidden="true" style="margin-right:0.3rem;"></i>{{ file.original_filename }}</span>
+              <button class="text-toggle" onclick="copyTextPreview()" id="text-copy-btn" aria-label="Copy file text">
+                <i class="fas fa-copy" aria-hidden="true"></i> Copy
+              </button>
+            </div>
+            <div class="text-content" id="text-preview-content" aria-live="polite">
+              <div style="text-align:center;padding:2rem;color:#94a3b8;"><i class="fas fa-spinner fa-spin" aria-hidden="true"></i> Loading…</div>
+            </div>
+          </div>
+
+          {% else %}
+          <!-- ── PDF viewer (pdf.js) ── -->
+          <div class="pdf-viewer" id="pdf-viewer">
+            <div class="pdf-controls">
+              <button class="pdf-nav-btn" onclick="pdfChangePage(-1)" id="pdf-prev-btn" aria-label="Previous page"><i class="fas fa-chevron-left" aria-hidden="true"></i></button>
+              <span class="pdf-page-info" id="pdf-page-info" aria-live="polite">Loading…</span>
+              <button class="pdf-nav-btn" onclick="pdfChangePage(1)" id="pdf-next-btn" aria-label="Next page"><i class="fas fa-chevron-right" aria-hidden="true"></i></button>
+            </div>
+            <div class="pdf-canvas-wrap" id="pdf-canvas-wrap">
+              <div style="text-align:center;padding:3rem;color:#94a3b8;">
+                <i class="fas fa-spinner fa-spin" aria-hidden="true" style="font-size:2rem;margin-bottom:0.75rem;"></i>
+                <p>Loading PDF…</p>
+              </div>
+            </div>
+          </div>
+          {% endif %}
+          <div style="font-size:0.75rem;color:#9ca3af;margin-top:0.4rem;text-align:right;">{{ 'Processed' if processed_file_exists else 'Original' }} version</div>
         {% else %}
           <div style="display:flex;flex-direction:column;align-items:center;justify-content:center;height:300px;background:#f9fafb;border-radius:0.375rem;color:#9ca3af;">
-            <i class="fas fa-file-pdf" style="font-size:3rem;margin-bottom:1rem;opacity:0.4;"></i>
+            <i class="fas fa-file" aria-hidden="true" style="font-size:3rem;margin-bottom:1rem;opacity:0.4;"></i>
             <p>No file available for preview</p>
           </div>
         {% endif %}
@@ -338,7 +445,7 @@
 </div>
 
 <script>
-  // Toggle inline OCR text visibility
+  // ── Toggle inline OCR text visibility ──
   function toggleOcrText() {
     var block = document.getElementById('ocr-text-block');
     var icon  = document.getElementById('ocr-toggle-icon');
@@ -357,7 +464,7 @@
     }
   }
 
-  // Copy OCR text to clipboard
+  // ── Copy OCR text to clipboard ──
   function copyOcrText() {
     var content = document.getElementById('ocr-text-content');
     if (!content) return;
@@ -369,8 +476,6 @@
       btn.innerHTML = '<i class="fas fa-check"></i> Copied!';
       setTimeout(function() { btn.innerHTML = orig; }, 2000);
     }).catch(function() {
-      // Legacy clipboard fallback for browsers without Secure Context / navigator.clipboard
-      // (pre-2018 environments, e.g. HTTP-only or older Safari). Retained for maximum compatibility.
       try {
         var ta = document.createElement('textarea');
         ta.value = text;
@@ -385,7 +490,7 @@
     });
   }
 
-  // On-demand text extraction (when ocr_text not in DB)
+  // ── On-demand text extraction (when ocr_text not in DB) ──
   var _textCache = null;
   function loadText(fileId) {
     var area = document.getElementById('text-load-area');
@@ -414,5 +519,156 @@
     pre.textContent = text;
     container.appendChild(pre);
   }
+
+  // ── PDF.js viewer ──
+  var _pdfState = { doc: null, page: 1, total: 0 };
+
+  function pdfInit(url) {
+    var wrap = document.getElementById('pdf-canvas-wrap');
+    if (!wrap) return;
+    pdfjsLib.getDocument(url).promise.then(function(pdf) {
+      _pdfState.doc = pdf;
+      _pdfState.total = pdf.numPages;
+      _pdfState.page = 1;
+      pdfRenderPage();
+    }).catch(function() {
+      wrap.innerHTML = '<div style="text-align:center;padding:2rem;color:#f87171;"><i class="fas fa-exclamation-triangle" style="font-size:2rem;margin-bottom:0.5rem;"></i><p>Failed to load PDF</p></div>';
+    });
+  }
+
+  function pdfRenderPage() {
+    var wrap = document.getElementById('pdf-canvas-wrap');
+    if (!_pdfState.doc || !wrap) return;
+    _pdfState.doc.getPage(_pdfState.page).then(function(page) {
+      var vp = page.getViewport({ scale: 1.0 });
+      var scale = Math.min(wrap.clientWidth / vp.width, 2.0);
+      var svp = page.getViewport({ scale: scale });
+      var canvas = document.createElement('canvas');
+      canvas.width = svp.width;
+      canvas.height = svp.height;
+      canvas.style.maxWidth = '100%';
+      canvas.style.height = 'auto';
+      wrap.innerHTML = '';
+      wrap.appendChild(canvas);
+      page.render({ canvasContext: canvas.getContext('2d'), viewport: svp });
+      pdfUpdateInfo();
+    });
+  }
+
+  function pdfChangePage(delta) {
+    var np = _pdfState.page + delta;
+    if (np >= 1 && np <= _pdfState.total) {
+      _pdfState.page = np;
+      pdfRenderPage();
+    }
+  }
+
+  function pdfUpdateInfo() {
+    var info = document.getElementById('pdf-page-info');
+    if (info) info.textContent = 'Page ' + _pdfState.page + ' of ' + _pdfState.total;
+    var prev = document.getElementById('pdf-prev-btn');
+    var next = document.getElementById('pdf-next-btn');
+    if (prev) prev.disabled = _pdfState.page <= 1;
+    if (next) next.disabled = _pdfState.page >= _pdfState.total;
+  }
+
+  // ── Image viewer with zoom / pan ──
+  var _imgScale = 1;
+
+  function imgZoom(factor) {
+    _imgScale = Math.max(0.25, Math.min(5, _imgScale * factor));
+    var img = document.getElementById('preview-img');
+    if (img) img.style.transform = 'scale(' + _imgScale + ')';
+    var label = document.getElementById('img-zoom-level');
+    if (label) label.textContent = Math.round(_imgScale * 100) + '%';
+  }
+
+  function imgReset() {
+    _imgScale = 1;
+    var img = document.getElementById('preview-img');
+    if (img) img.style.transform = 'scale(1)';
+    var label = document.getElementById('img-zoom-level');
+    if (label) label.textContent = '100%';
+  }
+
+  // Mouse-drag panning for image viewer
+  (function() {
+    var wrap = document.getElementById('img-wrap');
+    if (!wrap) return;
+    var dragging = false, startX, startY, scrollL, scrollT;
+    wrap.addEventListener('mousedown', function(e) {
+      dragging = true; wrap.classList.add('dragging');
+      startX = e.pageX - wrap.offsetLeft; startY = e.pageY - wrap.offsetTop;
+      scrollL = wrap.scrollLeft; scrollT = wrap.scrollTop;
+    });
+    wrap.addEventListener('mousemove', function(e) {
+      if (!dragging) return; e.preventDefault();
+      wrap.scrollLeft = scrollL - (e.pageX - wrap.offsetLeft - startX);
+      wrap.scrollTop  = scrollT - (e.pageY - wrap.offsetTop  - startY);
+    });
+    wrap.addEventListener('mouseup', function() { dragging = false; wrap.classList.remove('dragging'); });
+    wrap.addEventListener('mouseleave', function() { dragging = false; wrap.classList.remove('dragging'); });
+    // Mouse wheel zoom
+    wrap.addEventListener('wheel', function(e) {
+      e.preventDefault();
+      imgZoom(e.deltaY < 0 ? 1.1 : 0.9);
+    }, { passive: false });
+  })();
+
+  // ── Text file viewer ──
+  function loadTextPreview(url) {
+    var container = document.getElementById('text-preview-content');
+    if (!container) return;
+    fetch(url)
+      .then(function(r) { if (!r.ok) throw new Error('HTTP ' + r.status); return r.text(); })
+      .then(function(text) {
+        container.innerHTML = '';
+        var lines = text.split('\n');
+        for (var i = 0; i < lines.length; i++) {
+          var lineEl = document.createElement('div');
+          var numSpan = document.createElement('span');
+          numSpan.className = 'line-number';
+          numSpan.textContent = (i + 1) + '';
+          lineEl.appendChild(numSpan);
+          lineEl.appendChild(document.createTextNode(lines[i]));
+          container.appendChild(lineEl);
+        }
+      })
+      .catch(function() {
+        container.innerHTML = '<div style="color:#f87171;padding:1rem;">Failed to load file content</div>';
+      });
+  }
+
+  function copyTextPreview() {
+    var container = document.getElementById('text-preview-content');
+    if (!container) return;
+    var lines = container.querySelectorAll('div');
+    var text = [];
+    lines.forEach(function(line) {
+      var clone = line.cloneNode(true);
+      var num = clone.querySelector('.line-number');
+      if (num) num.remove();
+      text.push(clone.textContent);
+    });
+    var btn = document.getElementById('text-copy-btn');
+    var orig = btn.innerHTML;
+    navigator.clipboard.writeText(text.join('\n')).then(function() {
+      btn.innerHTML = '<i class="fas fa-check"></i> Copied!';
+      setTimeout(function() { btn.innerHTML = orig; }, 2000);
+    }).catch(function() {});
+  }
+
+  // ── Initialise on load ──
+  document.addEventListener('DOMContentLoaded', function() {
+    {% if (processed_file_exists or original_file_exists) and file %}
+      {% set pv = 'processed' if processed_file_exists else 'original' %}
+      {% set pm = file.mime_type or 'application/pdf' %}
+      {% if pm.startswith('text/') %}
+        loadTextPreview('/api/files/{{ file.id }}/preview?version={{ pv }}');
+      {% elif not pm.startswith('image/') %}
+        pdfInit('/api/files/{{ file.id }}/preview?version={{ pv }}');
+      {% endif %}
+    {% endif %}
+  });
 </script>
 {% endblock %}
diff --git a/frontend/templates/files.html b/frontend/templates/files.html
index 8daee476..a6e9c2f1 100644
--- a/frontend/templates/files.html
+++ b/frontend/templates/files.html
@@ -3,6 +3,11 @@
 
 {% block head_extra %}
   <script src="/static/js/common.js"></script>
+  <!-- PDF.js library for in-browser PDF preview -->
+  <script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.min.js"></script>
+  <script>
+    pdfjsLib.GlobalWorkerOptions.workerSrc = 'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js';
+  </script>
   <script>
     window.uploadConfig = {
       concurrency: {{ upload_concurrency }},
@@ -340,6 +345,80 @@
       border-radius: 0.25rem;
       margin-bottom: 1rem;
     }
+
+    /* ── Preview modal (side panel) ── */
+    .preview-overlay {
+      display: none; position: fixed; inset: 0; z-index: 1000;
+      background: rgba(0,0,0,0.5); justify-content: flex-end;
+    }
+    .preview-overlay.active { display: flex; }
+    .preview-panel {
+      width: 55%; max-width: 720px; min-width: 340px; height: 100%;
+      background: white; box-shadow: -4px 0 20px rgba(0,0,0,0.15);
+      display: flex; flex-direction: column; animation: slideIn 0.2s ease;
+    }
+    @keyframes slideIn { from { transform: translateX(100%); } to { transform: translateX(0); } }
+    @media (max-width: 768px) { .preview-panel { width: 100%; max-width: 100%; } }
+    .preview-panel-header {
+      display: flex; align-items: center; justify-content: space-between;
+      padding: 0.75rem 1rem; border-bottom: 1px solid #e5e7eb; flex-shrink: 0;
+    }
+    .preview-panel-header h3 { font-size: 1rem; font-weight: 600; color: #1f2937; margin: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+    .preview-panel-close {
+      background: none; border: none; cursor: pointer; padding: 0.5rem;
+      color: #6b7280; font-size: 1.25rem; min-height: 44px; min-width: 44px;
+      display: flex; align-items: center; justify-content: center;
+    }
+    .preview-panel-close:hover { color: #1f2937; }
+    .preview-panel-body { flex: 1; overflow: auto; padding: 0; background: #f9fafb; }
+    .preview-panel-footer {
+      display: flex; align-items: center; justify-content: center; gap: 0.75rem;
+      padding: 0.75rem 1rem; border-top: 1px solid #e5e7eb; flex-shrink: 0;
+    }
+    .preview-panel-footer a, .preview-panel-footer button {
+      display: inline-flex; align-items: center; gap: 0.3rem;
+      padding: 0.4rem 0.9rem; border-radius: 0.25rem; font-size: 0.85rem; font-weight: 600;
+      text-decoration: none; cursor: pointer; border: 1px solid #d1d5db; background: white; color: #374151;
+      min-height: 40px;
+    }
+    .preview-panel-footer a:hover, .preview-panel-footer button:hover { background: #f3f4f6; }
+    /* PDF controls inside preview modal */
+    .pm-pdf-controls {
+      display: flex; align-items: center; justify-content: center; gap: 0.5rem;
+      padding: 0.5rem; background: #f1f5f9; border-bottom: 1px solid #e2e8f0;
+    }
+    .pm-pdf-controls button {
+      padding: 0.3rem 0.6rem; border: 1px solid #cbd5e1; border-radius: 0.25rem;
+      background: white; cursor: pointer; font-size: 0.8rem; min-height: 36px; min-width: 36px;
+    }
+    .pm-pdf-controls button:disabled { opacity: 0.4; cursor: default; }
+    .pm-canvas-wrap { display: flex; justify-content: center; padding: 0.5rem; min-height: 300px; overflow: auto; }
+    .pm-canvas-wrap canvas { max-width: 100%; height: auto; }
+    /* Image in preview modal */
+    .pm-img-controls {
+      display: flex; align-items: center; justify-content: center; gap: 0.5rem;
+      padding: 0.5rem; background: #f1f5f9; border-bottom: 1px solid #e2e8f0;
+    }
+    .pm-img-controls button {
+      padding: 0.3rem 0.6rem; border: 1px solid #cbd5e1; border-radius: 0.25rem;
+      background: white; cursor: pointer; font-size: 0.85rem; min-height: 36px; min-width: 36px;
+    }
+    .pm-img-wrap {
+      display: flex; justify-content: center; align-items: center;
+      overflow: auto; cursor: grab; flex: 1; padding: 0.5rem; background: #525659;
+    }
+    .pm-img-wrap.dragging { cursor: grabbing; }
+    .pm-img-wrap img { transition: transform 0.15s ease; max-width: 100%; height: auto; }
+    /* Text in preview modal */
+    .pm-text-content {
+      background: #1e293b; color: #e2e8f0; padding: 1rem; font-family: 'SFMono-Regular', Consolas, monospace;
+      font-size: 0.82rem; line-height: 1.65; min-height: 300px; white-space: pre-wrap; word-break: break-word;
+      tab-size: 4;
+    }
+    .pm-line-number {
+      display: inline-block; width: 3.5em; color: #64748b; text-align: right;
+      margin-right: 1em; user-select: none; font-size: 0.75rem;
+    }
   </style>
 {% endblock %}
 
@@ -582,6 +661,9 @@
           <td>{{ file.created_at.strftime('%Y-%m-%d %H:%M:%S') if file.created_at else 'N/A' }}</td>
           <td>
             <div style="display: flex; align-items: center;">
+              <button onclick="openPreviewModal({{ file.id }}, '{{ file.mime_type or '' }}', '{{ file.original_filename | e }}', event)" class="action-btn" title="Quick preview" aria-label="Preview {{ file.original_filename }}" style="min-height:44px;min-width:44px;">
+                <i class="fas fa-eye" aria-hidden="true"></i>
+              </button>
               <button onclick="viewFileDetail({{ file.id }}, event)" class="action-btn" title="View details" aria-label="View details for {{ file.original_filename }}" style="min-height:44px;min-width:44px;">
                 <i class="fas fa-info-circle" aria-hidden="true"></i>
               </button>
@@ -621,6 +703,9 @@
         <div class="flex flex-col items-end gap-2 flex-shrink-0">
           <span class="status-badge status-{{ file.processing_status }}">{{ file.processing_status | title }}</span>
           <div class="flex gap-1" role="group" aria-label="File actions" onclick="event.stopPropagation();" onkeydown="event.stopPropagation();">
+            <button onclick="openPreviewModal({{ file.id }}, '{{ file.mime_type or '' }}', '{{ file.original_filename | e }}', event)" class="action-btn" title="Quick preview" aria-label="Preview {{ file.original_filename }}" style="min-height:44px;min-width:44px;">
+              <i class="fas fa-eye" aria-hidden="true"></i>
+            </button>
             <button onclick="viewFileDetail({{ file.id }}, event)" class="action-btn" title="View details" aria-label="View details for {{ file.original_filename }}" style="min-height:44px;min-width:44px;">
               <i class="fas fa-info-circle" aria-hidden="true"></i>
             </button>
@@ -676,6 +761,24 @@
     </div>
   </div>
 
+  <!-- Preview side-panel modal -->
+  <div id="previewOverlay" class="preview-overlay" role="dialog" aria-modal="true" aria-labelledby="previewTitle">
+    <div class="preview-panel">
+      <div class="preview-panel-header">
+        <h3 id="previewTitle">Preview</h3>
+        <button class="preview-panel-close" onclick="closePreviewModal()" aria-label="Close preview">
+          <i class="fas fa-times" aria-hidden="true"></i>
+        </button>
+      </div>
+      <div class="preview-panel-body" id="previewBody" aria-live="polite">
+        <div style="display:flex;align-items:center;justify-content:center;height:100%;color:#9ca3af;">
+          <i class="fas fa-spinner fa-spin" aria-hidden="true" style="font-size:2rem;"></i>
+        </div>
+      </div>
+      <div class="preview-panel-footer" id="previewFooter"></div>
+    </div>
+  </div>
+
   <script>
     // Modal functionality
     const deleteModal = document.getElementById('deleteModal');
@@ -694,6 +797,174 @@
       window.location.href = `/files/${fileId}/detail`;
     }
 
+    // ── Preview modal ──
+    let _pmPdf = { doc: null, page: 1, total: 0 };
+    let _pmImgScale = 1;
+
+    function openPreviewModal(fileId, mime, filename, event) {
+      if (event) event.stopPropagation();
+      const overlay = document.getElementById('previewOverlay');
+      const title = document.getElementById('previewTitle');
+      const body = document.getElementById('previewBody');
+      const footer = document.getElementById('previewFooter');
+      title.textContent = filename || 'Preview';
+      body.innerHTML = '<div style="display:flex;align-items:center;justify-content:center;height:300px;color:#9ca3af;"><i class="fas fa-spinner fa-spin" style="font-size:2rem;"></i></div>';
+      footer.innerHTML = '';
+      _pmPdf = { doc: null, page: 1, total: 0 };
+      _pmImgScale = 1;
+      overlay.classList.add('active');
+      document.body.style.overflow = 'hidden';
+
+      const previewUrl = `/api/files/${fileId}/preview?version=processed`;
+
+      footer.innerHTML =
+        `<a href="/files/${fileId}" aria-label="Open full view"><i class="fas fa-expand" aria-hidden="true"></i> Full view</a>` +
+        `<a href="/api/files/${fileId}/download?version=processed" aria-label="Download file"><i class="fas fa-download" aria-hidden="true"></i> Download</a>`;
+
+      if (mime && mime.startsWith('image/')) {
+        _pmRenderImage(body, previewUrl, filename);
+      } else if (mime && mime.startsWith('text/')) {
+        _pmRenderText(body, previewUrl);
+      } else {
+        _pmRenderPdf(body, previewUrl);
+      }
+    }
+
+    function closePreviewModal() {
+      const overlay = document.getElementById('previewOverlay');
+      overlay.classList.remove('active');
+      document.body.style.overflow = '';
+      _pmPdf = { doc: null, page: 1, total: 0 };
+    }
+
+    // PDF rendering inside preview modal
+    function _pmRenderPdf(body, url) {
+      body.innerHTML =
+        '<div class="pm-pdf-controls">' +
+          '<button onclick="_pmPdfPage(-1)" id="pm-prev" aria-label="Previous page"><i class="fas fa-chevron-left" aria-hidden="true"></i></button>' +
+          '<span id="pm-page-info" style="font-size:0.8rem;min-width:100px;text-align:center;">Loading…</span>' +
+          '<button onclick="_pmPdfPage(1)" id="pm-next" aria-label="Next page"><i class="fas fa-chevron-right" aria-hidden="true"></i></button>' +
+        '</div>' +
+        '<div class="pm-canvas-wrap" id="pm-canvas-wrap"><div style="text-align:center;padding:3rem;color:#94a3b8;"><i class="fas fa-spinner fa-spin" style="font-size:2rem;"></i></div></div>';
+
+      pdfjsLib.getDocument(url).promise.then(function(pdf) {
+        _pmPdf.doc = pdf;
+        _pmPdf.total = pdf.numPages;
+        _pmPdf.page = 1;
+        _pmPdfRender();
+      }).catch(function() {
+        document.getElementById('pm-canvas-wrap').innerHTML = '<div style="text-align:center;padding:2rem;color:#f87171;"><i class="fas fa-exclamation-triangle" style="font-size:2rem;margin-bottom:0.5rem;"></i><p>Failed to load PDF</p></div>';
+      });
+    }
+
+    function _pmPdfRender() {
+      var wrap = document.getElementById('pm-canvas-wrap');
+      if (!_pmPdf.doc || !wrap) return;
+      _pmPdf.doc.getPage(_pmPdf.page).then(function(page) {
+        var vp = page.getViewport({ scale: 1.0 });
+        var scale = Math.min((wrap.clientWidth - 16) / vp.width, 2.0);
+        var svp = page.getViewport({ scale: scale });
+        var canvas = document.createElement('canvas');
+        canvas.width = svp.width;
+        canvas.height = svp.height;
+        canvas.style.maxWidth = '100%';
+        canvas.style.height = 'auto';
+        wrap.innerHTML = '';
+        wrap.appendChild(canvas);
+        page.render({ canvasContext: canvas.getContext('2d'), viewport: svp });
+        _pmPdfUpdateInfo();
+      });
+    }
+
+    function _pmPdfPage(delta) {
+      var np = _pmPdf.page + delta;
+      if (np >= 1 && np <= _pmPdf.total) { _pmPdf.page = np; _pmPdfRender(); }
+    }
+
+    function _pmPdfUpdateInfo() {
+      var info = document.getElementById('pm-page-info');
+      if (info) info.textContent = 'Page ' + _pmPdf.page + ' of ' + _pmPdf.total;
+      var prev = document.getElementById('pm-prev');
+      var next = document.getElementById('pm-next');
+      if (prev) prev.disabled = _pmPdf.page <= 1;
+      if (next) next.disabled = _pmPdf.page >= _pmPdf.total;
+    }
+
+    // Image rendering inside preview modal
+    function _pmRenderImage(body, url, alt) {
+      body.innerHTML =
+        '<div class="pm-img-controls">' +
+          '<button onclick="_pmImgZoom(1.25)" title="Zoom in" aria-label="Zoom in"><i class="fas fa-search-plus" aria-hidden="true"></i></button>' +
+          '<button onclick="_pmImgZoom(0.8)" title="Zoom out" aria-label="Zoom out"><i class="fas fa-search-minus" aria-hidden="true"></i></button>' +
+          '<button onclick="_pmImgReset()" title="Reset" aria-label="Reset zoom"><i class="fas fa-expand" aria-hidden="true"></i></button>' +
+          '<span id="pm-zoom-level" style="font-size:0.8rem;color:#6b7280;">100%</span>' +
+        '</div>' +
+        '<div class="pm-img-wrap" id="pm-img-wrap"><img id="pm-preview-img" src="' + url + '" alt="' + (alt || 'Preview') + '" draggable="false" style="max-width:100%;height:auto;"></div>';
+      // Drag-pan
+      var wrap = document.getElementById('pm-img-wrap');
+      if (wrap) {
+        var dragging = false, sX, sY, sL, sT;
+        wrap.addEventListener('mousedown', function(e){ dragging=true; wrap.classList.add('dragging'); sX=e.pageX-wrap.offsetLeft; sY=e.pageY-wrap.offsetTop; sL=wrap.scrollLeft; sT=wrap.scrollTop; });
+        wrap.addEventListener('mousemove', function(e){ if(!dragging) return; e.preventDefault(); wrap.scrollLeft=sL-(e.pageX-wrap.offsetLeft-sX); wrap.scrollTop=sT-(e.pageY-wrap.offsetTop-sY); });
+        wrap.addEventListener('mouseup', function(){ dragging=false; wrap.classList.remove('dragging'); });
+        wrap.addEventListener('mouseleave', function(){ dragging=false; wrap.classList.remove('dragging'); });
+        wrap.addEventListener('wheel', function(e){ e.preventDefault(); _pmImgZoom(e.deltaY<0?1.1:0.9); }, {passive:false});
+      }
+    }
+
+    function _pmImgZoom(factor) {
+      _pmImgScale = Math.max(0.25, Math.min(5, _pmImgScale * factor));
+      var img = document.getElementById('pm-preview-img');
+      if (img) img.style.transform = 'scale(' + _pmImgScale + ')';
+      var lbl = document.getElementById('pm-zoom-level');
+      if (lbl) lbl.textContent = Math.round(_pmImgScale * 100) + '%';
+    }
+
+    function _pmImgReset() {
+      _pmImgScale = 1;
+      var img = document.getElementById('pm-preview-img');
+      if (img) img.style.transform = 'scale(1)';
+      var lbl = document.getElementById('pm-zoom-level');
+      if (lbl) lbl.textContent = '100%';
+    }
+
+    // Text rendering inside preview modal
+    function _pmRenderText(body, url) {
+      body.innerHTML = '<div class="pm-text-content" id="pm-text-content"><div style="text-align:center;padding:2rem;color:#94a3b8;"><i class="fas fa-spinner fa-spin"></i> Loading…</div></div>';
+      fetch(url)
+        .then(function(r) { if (!r.ok) throw new Error('HTTP ' + r.status); return r.text(); })
+        .then(function(text) {
+          var container = document.getElementById('pm-text-content');
+          if (!container) return;
+          container.innerHTML = '';
+          var lines = text.split('\n');
+          for (var i = 0; i < lines.length; i++) {
+            var div = document.createElement('div');
+            var num = document.createElement('span');
+            num.className = 'pm-line-number';
+            num.textContent = (i + 1) + '';
+            div.appendChild(num);
+            div.appendChild(document.createTextNode(lines[i]));
+            container.appendChild(div);
+          }
+        })
+        .catch(function() {
+          var c = document.getElementById('pm-text-content');
+          if (c) c.innerHTML = '<div style="color:#f87171;padding:1rem;">Failed to load file</div>';
+        });
+    }
+
+    // Close preview on overlay click or Escape
+    document.getElementById('previewOverlay').addEventListener('click', function(e) {
+      if (e.target === this) closePreviewModal();
+    });
+    document.addEventListener('keydown', function(e) {
+      if (e.key === 'Escape') {
+        var overlay = document.getElementById('previewOverlay');
+        if (overlay && overlay.classList.contains('active')) closePreviewModal();
+      }
+    });
+
     cancelDelete.addEventListener('click', () => {
       deleteModal.style.display = 'none';
     });