diff --git a/app/tasks/process_document.py b/app/tasks/process_document.py
index 05cfa74b..8b9f5921 100644
--- a/app/tasks/process_document.py
+++ b/app/tasks/process_document.py
@@ -9,7 +9,9 @@ import PyPDF2  # Replace fitz with PyPDF2
 
 from app.config import settings
 from app.tasks.retry_config import BaseTaskWithRetry
-from app.tasks.process_with_azure_document_intelligence import process_with_azure_document_intelligence
+from app.tasks.process_with_azure_document_intelligence import (
+    process_with_azure_document_intelligence,
+)
 from app.tasks.extract_metadata_with_gpt import extract_metadata_with_gpt
 from app.celery_app import celery
 from app.database import SessionLocal
@@ -33,7 +35,12 @@ def process_document(self, original_local_file: str):
     """
     task_id = self.request.id
     logger.info(f"[{task_id}] Starting document processing: {original_local_file}")
-    log_task_progress(task_id, "process_document", "in_progress", f"Processing file: {original_local_file}")
+    log_task_progress(
+        task_id,
+        "process_document",
+        "in_progress",
+        f"Processing file: {original_local_file}",
+    )
 
     if not os.path.exists(original_local_file):
         logger.error(f"[{task_id}] File {original_local_file} not found.")
@@ -49,25 +56,42 @@ def process_document(self, original_local_file: str):
     mime_type, _ = mimetypes.guess_type(original_local_file)
     if not mime_type:
         mime_type = "application/octet-stream"
-    
-    logger.info(f"[{task_id}] File hash: {filehash[:10]}..., Size: {file_size} bytes, MIME: {mime_type}")
-    log_task_progress(task_id, "hash_file", "success", f"Hash: {filehash[:10]}..., Size: {file_size} bytes")
+
+    logger.info(
+        f"[{task_id}] File hash: {filehash[:10]}..., Size: {file_size} bytes, MIME: {mime_type}"
+    )
+    log_task_progress(
+        task_id,
+        "hash_file",
+        "success",
+        f"Hash: {filehash[:10]}..., Size: {file_size} bytes",
+    )
 
     # Acquire DB session in the task
     with SessionLocal() as db:
         existing = db.query(FileRecord).filter_by(filehash=filehash).one_or_none()
         if existing:
-            logger.info(f"[{task_id}] Duplicate file detected (hash={filehash[:10]}...) Skipping processing.")
-            log_task_progress(task_id, "process_document", "success", "Duplicate file detected, skipping", file_id=existing.id)
+            logger.info(
+                f"[{task_id}] Duplicate file detected (hash={filehash[:10]}...) Skipping processing."
+            )
+            log_task_progress(
+                task_id,
+                "process_document",
+                "success",
+                "Duplicate file detected, skipping",
+                file_id=existing.id,
+            )
             return {
                 "status": "duplicate_file",
                 "file_id": existing.id,
-                "detail": "File already processed."
+                "detail": "File already processed.",
             }
 
         # Not a duplicate -> insert a new record
         logger.info(f"[{task_id}] Creating new file record in database")
-        log_task_progress(task_id, "create_file_record", "in_progress", "Creating file record")
+        log_task_progress(
+            task_id, "create_file_record", "in_progress", "Creating file record"
+        )
         new_record = FileRecord(
             filehash=filehash,
             original_filename=original_filename,
@@ -79,7 +103,13 @@ def process_document(self, original_local_file: str):
         db.commit()
         db.refresh(new_record)
         logger.info(f"[{task_id}] File record created with ID: {new_record.id}")
-        log_task_progress(task_id, "create_file_record", "success", f"File record ID: {new_record.id}", file_id=new_record.id)
+        log_task_progress(
+            task_id,
+            "create_file_record",
+            "success",
+            f"File record ID: {new_record.id}",
+            file_id=new_record.id,
+        )
 
         # 1. Generate a UUID-based filename and place it in /workdir/tmp
         file_ext = os.path.splitext(original_local_file)[1]
@@ -91,19 +121,40 @@ def process_document(self, original_local_file: str):
         new_local_path = os.path.join(tmp_dir, new_filename)
 
         logger.info(f"[{task_id}] Copying file to: {new_local_path}")
-        log_task_progress(task_id, "copy_file", "in_progress", f"Copying file to {new_filename}", file_id=new_record.id)
+        log_task_progress(
+            task_id,
+            "copy_file",
+            "in_progress",
+            f"Copying file to {new_filename}",
+            file_id=new_record.id,
+        )
         # Copy the file instead of moving it
         shutil.copy(original_local_file, new_local_path)
-        log_task_progress(task_id, "copy_file", "success", f"File copied to {new_filename}", file_id=new_record.id)
+        log_task_progress(
+            task_id,
+            "copy_file",
+            "success",
+            f"File copied to {new_filename}",
+            file_id=new_record.id,
+        )
 
         # Update the DB with final local filename
         new_record.local_filename = new_local_path
         db.commit()
 
+        # Store file_id before session closes to avoid DetachedInstanceError
+        file_id = new_record.id
+
     # 2. Check for embedded text (outside the DB session to avoid long open transactions)
     logger.info(f"[{task_id}] Checking for embedded text in PDF")
-    log_task_progress(task_id, "check_text", "in_progress", "Checking for embedded text", file_id=new_record.id)
-    with open(new_local_path, 'rb') as file:
+    log_task_progress(
+        task_id,
+        "check_text",
+        "in_progress",
+        "Checking for embedded text",
+        file_id=file_id,
+    )
+    with open(new_local_path, "rb") as file:
         pdf_reader = PyPDF2.PdfReader(file)
         has_text = False
         for page in pdf_reader.pages:
@@ -112,30 +163,74 @@ def process_document(self, original_local_file: str):
                 break
 
     if has_text:
-        logger.info(f"[{task_id}] PDF {original_local_file} contains embedded text. Processing locally.")
-        log_task_progress(task_id, "check_text", "success", "Embedded text found, extracting locally", file_id=new_record.id)
+        logger.info(
+            f"[{task_id}] PDF {original_local_file} contains embedded text. Processing locally."
+        )
+        log_task_progress(
+            task_id,
+            "check_text",
+            "success",
+            "Embedded text found, extracting locally",
+            file_id=file_id,
+        )
 
         # Extract text locally
         logger.info(f"[{task_id}] Extracting text from PDF")
-        log_task_progress(task_id, "extract_text", "in_progress", "Extracting text locally", file_id=new_record.id)
+        log_task_progress(
+            task_id,
+            "extract_text",
+            "in_progress",
+            "Extracting text locally",
+            file_id=file_id,
+        )
         extracted_text = ""
-        with open(new_local_path, 'rb') as file:
+        with open(new_local_path, "rb") as file:
             pdf_reader = PyPDF2.PdfReader(file)
             for page in pdf_reader.pages:
                 extracted_text += page.extract_text() + "\n"
-        
+
         logger.info(f"[{task_id}] Extracted {len(extracted_text)} characters")
-        log_task_progress(task_id, "extract_text", "success", f"Extracted {len(extracted_text)} characters", file_id=new_record.id)
+        log_task_progress(
+            task_id,
+            "extract_text",
+            "success",
+            f"Extracted {len(extracted_text)} characters",
+            file_id=file_id,
+        )
 
         # Call metadata extraction directly
         logger.info(f"[{task_id}] Queueing metadata extraction")
-        log_task_progress(task_id, "process_document", "success", "Queued for metadata extraction", file_id=new_record.id)
-        extract_metadata_with_gpt.delay(new_filename, extracted_text, new_record.id)
-        return {"file": new_local_path, "status": "Text extracted locally", "file_id": new_record.id}
+        log_task_progress(
+            task_id,
+            "process_document",
+            "success",
+            "Queued for metadata extraction",
+            file_id=file_id,
+        )
+        extract_metadata_with_gpt.delay(new_filename, extracted_text, file_id)
+        return {
+            "file": new_local_path,
+            "status": "Text extracted locally",
+            "file_id": file_id,
+        }
 
     # 3. If no embedded text, queue Azure Document Intelligence processing
-    logger.info(f"[{task_id}] No embedded text found. Queueing Azure Document Intelligence processing")
-    log_task_progress(task_id, "check_text", "success", "No embedded text, queuing OCR", file_id=new_record.id)
-    log_task_progress(task_id, "process_document", "success", "Queued for OCR processing", file_id=new_record.id)
-    process_with_azure_document_intelligence.delay(new_filename, new_record.id)
-    return {"file": new_local_path, "status": "Queued for OCR", "file_id": new_record.id}
+    logger.info(
+        f"[{task_id}] No embedded text found. Queueing Azure Document Intelligence processing"
+    )
+    log_task_progress(
+        task_id,
+        "check_text",
+        "success",
+        "No embedded text, queuing OCR",
+        file_id=file_id,
+    )
+    log_task_progress(
+        task_id,
+        "process_document",
+        "success",
+        "Queued for OCR processing",
+        file_id=file_id,
+    )
+    process_with_azure_document_intelligence.delay(new_filename, file_id)
+    return {"file": new_local_path, "status": "Queued for OCR", "file_id": file_id}
diff --git a/tests/test_process_document.py b/tests/test_process_document.py
new file mode 100644
index 00000000..84112867
--- /dev/null
+++ b/tests/test_process_document.py
@@ -0,0 +1,244 @@
+"""
+Unit tests for the process_document task.
+
+These tests verify that the process_document task correctly handles file processing
+and doesn't cause DetachedInstanceError when accessing database objects.
+"""
+
+import os
+import pytest
+from unittest.mock import patch, MagicMock
+from sqlalchemy.orm import Session
+
+from app.tasks.process_document import process_document
+from app.models import FileRecord
+
+
+@pytest.mark.unit
+@pytest.mark.requires_db
+def test_process_document_stores_file_id_before_session_closes(db_session, tmp_path):
+    """
+    Test that process_document stores file_id before the database session closes.
+    This prevents DetachedInstanceError when accessing the file_id after the session ends.
+    """
+    # Create a test PDF file with embedded text
+    test_pdf = tmp_path / "test.pdf"
+    pdf_content = b"""%PDF-1.4
+1 0 obj
+<<
+/Type /Catalog
+/Pages 2 0 R
+>>
+endobj
+2 0 obj
+<<
+/Type /Pages
+/Kids [3 0 R]
+/Count 1
+>>
+endobj
+3 0 obj
+<<
+/Type /Page
+/Parent 2 0 R
+/MediaBox [0 0 612 792]
+/Resources <<
+/Font <<
+/F1 <<
+/Type /Font
+/Subtype /Type1
+/BaseFont /Helvetica
+>>
+>>
+>>
+/Contents 4 0 R
+>>
+endobj
+4 0 obj
+<<
+/Length 44
+>>
+stream
+BT
+/F1 12 Tf
+100 700 Td
+(Test content) Tj
+ET
+endstream
+endobj
+xref
+0 5
+0000000000 65535 f
+0000000009 00000 n
+0000000058 00000 n
+0000000115 00000 n
+0000000306 00000 n
+trailer
+<<
+/Size 5
+/Root 1 0 R
+>>
+startxref
+399
+%%EOF
+"""
+    test_pdf.write_bytes(pdf_content)
+
+    # Mock environment and dependencies
+    with patch("app.tasks.process_document.SessionLocal") as mock_session_local, patch(
+        "app.tasks.process_document.settings"
+    ) as mock_settings, patch("app.tasks.process_document.log_task_progress"), patch(
+        "app.tasks.process_document.extract_metadata_with_gpt"
+    ) as mock_extract:
+
+        # Setup mocks
+        mock_settings.workdir = str(tmp_path)
+        mock_session_local.return_value.__enter__.return_value = db_session
+        mock_session_local.return_value.__exit__.return_value = None
+        mock_extract.delay = MagicMock()
+
+        # Get the actual function from the task (skip decorators)
+        # The task function signature is: def process_document(self, original_local_file: str)
+        task_run_func = process_document.run
+
+        # Call the task's run method directly
+        result = task_run_func(str(test_pdf))
+
+        # Verify that the task completed successfully
+        assert "file_id" in result
+        assert result["status"] == "Text extracted locally"
+
+        # Verify that a FileRecord was created
+        file_record = db_session.query(FileRecord).first()
+        assert file_record is not None
+        assert file_record.original_filename == "test.pdf"
+
+        # Verify that extract_metadata_with_gpt was called with the file_id
+        # This would fail if file_id wasn't extracted before the session closed
+        mock_extract.delay.assert_called_once()
+        call_args = mock_extract.delay.call_args
+        assert call_args[0][2] == file_record.id  # Third argument should be file_id
+
+
+@pytest.mark.unit
+@pytest.mark.requires_db
+def test_process_document_duplicate_file(db_session, tmp_path):
+    """
+    Test that duplicate files are detected and processing is skipped.
+    """
+    # Create a test PDF file
+    test_pdf = tmp_path / "test.pdf"
+    test_pdf.write_bytes(b"test content")
+
+    # Pre-create a FileRecord with the same hash
+    from app.utils import hash_file
+
+    filehash = hash_file(str(test_pdf))
+
+    existing_record = FileRecord(
+        filehash=filehash,
+        original_filename="existing.pdf",
+        local_filename="/tmp/existing.pdf",
+        file_size=100,
+        mime_type="application/pdf",
+    )
+    db_session.add(existing_record)
+    db_session.commit()
+    existing_id = existing_record.id
+
+    # Mock environment and dependencies
+    with patch("app.tasks.process_document.SessionLocal") as mock_session_local, patch(
+        "app.tasks.process_document.log_task_progress"
+    ):
+
+        # Setup mocks
+        mock_session_local.return_value.__enter__.return_value = db_session
+        mock_session_local.return_value.__exit__.return_value = None
+
+        # Call the task's run method directly
+        result = process_document.run(str(test_pdf))
+
+        # Verify that duplicate was detected
+        assert result["status"] == "duplicate_file"
+        assert result["file_id"] == existing_id
+
+        # Verify only one FileRecord exists
+        assert db_session.query(FileRecord).count() == 1
+
+
+@pytest.mark.unit
+@pytest.mark.requires_db
+def test_process_document_queues_ocr_for_image_pdf(db_session, tmp_path):
+    """
+    Test that PDFs without embedded text are queued for OCR processing.
+    """
+    # Create a test PDF file without text
+    test_pdf = tmp_path / "test_image.pdf"
+    pdf_content = b"""%PDF-1.4
+1 0 obj
+<<
+/Type /Catalog
+/Pages 2 0 R
+>>
+endobj
+2 0 obj
+<<
+/Type /Pages
+/Kids [3 0 R]
+/Count 1
+>>
+endobj
+3 0 obj
+<<
+/Type /Page
+/Parent 2 0 R
+/MediaBox [0 0 612 792]
+>>
+endobj
+xref
+0 4
+0000000000 65535 f
+0000000009 00000 n
+0000000058 00000 n
+0000000115 00000 n
+trailer
+<<
+/Size 4
+/Root 1 0 R
+>>
+startxref
+197
+%%EOF
+"""
+    test_pdf.write_bytes(pdf_content)
+
+    # Mock environment and dependencies
+    with patch("app.tasks.process_document.SessionLocal") as mock_session_local, patch(
+        "app.tasks.process_document.settings"
+    ) as mock_settings, patch("app.tasks.process_document.log_task_progress"), patch(
+        "app.tasks.process_document.process_with_azure_document_intelligence"
+    ) as mock_azure:
+
+        # Setup mocks
+        mock_settings.workdir = str(tmp_path)
+        mock_session_local.return_value.__enter__.return_value = db_session
+        mock_session_local.return_value.__exit__.return_value = None
+        mock_azure.delay = MagicMock()
+
+        # Call the task's run method directly
+        result = process_document.run(str(test_pdf))
+
+        # Verify that OCR was queued
+        assert result["status"] == "Queued for OCR"
+        assert "file_id" in result
+
+        # Verify that process_with_azure_document_intelligence was called with file_id
+        mock_azure.delay.assert_called_once()
+        call_args = mock_azure.delay.call_args
+
+        # Verify a FileRecord was created
+        file_record = db_session.query(FileRecord).first()
+        assert file_record is not None
+
+        # The second argument should be the file_id
+        assert call_args[0][1] == file_record.id