docs: clarify PDF splitting is page-based, not byte-based

- Add prominent documentation that splitting uses page boundaries
- Update docstring with IMPORTANT note about page-level splitting
- Add test to validate split PDFs are valid and readable
- Update ConfigurationGuide.md to emphasize page-based approach
- Update SECURITY_AUDIT.md with implementation details
- Ensures users understand no risk of corrupted PDFs

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

SECURITY_AUDIT.md

@@ -150,7 +150,10 @@ This document tracks security vulnerabilities found in DocuElevate and their rem
 **Fix:** Implemented configurable file upload size limits with the following features:
 - `MAX_UPLOAD_SIZE`: Maximum file upload size in bytes (default: 1GB)
 - `MAX_SINGLE_FILE_SIZE`: Optional maximum size for a single file chunk
-- Automatic file splitting for large PDFs when max_single_file_size is configured
+- **Automatic page-based PDF splitting** for large PDFs when max_single_file_size is configured
+  - Splits PDFs at **page boundaries** using PyPDF2, NOT by byte position
+  - Each output file is a structurally valid, complete PDF
+  - No risk of corrupted or broken PDF files
 - Split files are processed sequentially to prevent overwhelming the system
 - Clear error messages referencing SECURITY_AUDIT.md for configuration details
 

app/utils/file_splitting.py

@@ -19,8 +19,16 @@ def split_pdf_by_size(pdf_path: str, max_size_bytes: int, output_dir: Optional[s
     """
     Split a PDF file into multiple smaller PDF files based on size constraints.
 
-    The function splits the PDF by distributing pages across multiple output files,
+    IMPORTANT: This function splits PDFs at PAGE BOUNDARIES, not by byte position.
-    ensuring each output file stays under the specified size limit.
+    It uses PyPDF2 to properly parse the PDF structure and distribute complete pages
+    across multiple valid output PDFs. This ensures:
+    - All output files are structurally valid and readable PDFs
+    - No corrupted or broken PDF files are created
+    - Each output file contains complete pages from the original document
+
+    The function adds pages to the current output file until adding another page
+    would exceed the size limit, then starts a new output file. This is NOT a
+    simple byte-level file split - it respects PDF page boundaries.
 
     Args:
         pdf_path: Path to the PDF file to split
@@ -28,15 +36,18 @@ def split_pdf_by_size(pdf_path: str, max_size_bytes: int, output_dir: Optional[s
         output_dir: Directory to save split files. If None, uses same directory as input file.
 
     Returns:
-        List of paths to the generated PDF files (in order)
+        List of paths to the generated PDF files (in order). Each file is a valid PDF
+        containing complete pages from the original document.
 
     Raises:
         FileNotFoundError: If the input PDF file doesn't exist
         ValueError: If max_size_bytes is too small to fit even one page
 
     Example:
-        >>> split_files = split_pdf_by_size("large.pdf", 50 * 1024 * 1024)  # 50MB max
+        >>> # Split a large PDF into chunks of max 50MB each
+        >>> split_files = split_pdf_by_size("large.pdf", 50 * 1024 * 1024)
         >>> print(f"Split into {len(split_files)} files")
+        >>> # Each file is a valid PDF with complete pages
     """
     # Validate input file exists
     if not os.path.exists(pdf_path):

docs/ConfigurationGuide.md

@@ -57,6 +57,11 @@ MAX_SINGLE_FILE_SIZE=524288000
 
 **File Splitting Behavior:**
 - When `MAX_SINGLE_FILE_SIZE` is configured and a PDF exceeds this size, it is automatically split into smaller chunks
+- **IMPORTANT:** Splitting is done at **PAGE BOUNDARIES**, not by byte position
+  - Uses PyPDF2 to properly parse PDF structure
+  - Each output file is a complete, valid PDF containing whole pages
+  - No risk of corrupted or broken PDF files
+  - Pages are distributed across output files to stay under size limit
 - Each chunk is processed sequentially as a separate task
 - Only works for PDF files (images and office documents are converted to PDF first)
 - Original file is removed after successful splitting

tests/test_file_splitting.py

@@ -181,6 +181,44 @@ class TestSplitPdfBySize:
             if os.path.exists(split_file):
                 os.remove(split_file)
 
+    def test_split_pdfs_are_valid_and_readable(self, sample_multipage_pdf):
+        """Test that split PDFs are valid, complete PDFs that can be opened and read.
+
+        This test verifies that PDF splitting is done at PAGE BOUNDARIES,
+        not by byte position, ensuring no corrupted/broken PDFs are created.
+        """
+        max_size = 5000  # Small size to force splitting
+
+        split_files = split_pdf_by_size(sample_multipage_pdf, max_size)
+
+        try:
+            # Verify each split file is a valid, readable PDF
+            for split_file in split_files:
+                assert os.path.exists(split_file), f"Split file {split_file} should exist"
+
+                # Try to open and read the PDF - this will fail if PDF is corrupted
+                try:
+                    reader = PdfReader(split_file)
+                    # Verify it has pages (not an empty or broken PDF)
+                    assert len(reader.pages) > 0, f"Split PDF {split_file} should have pages"
+
+                    # Try to access first page content to ensure PDF structure is valid
+                    first_page = reader.pages[0]
+                    # If the PDF was corrupted by byte-splitting, this would raise an error
+                    _ = first_page.extract_text()  # This validates PDF structure
+
+                except Exception as e:
+                    pytest.fail(
+                        f"Split PDF {split_file} is corrupted or unreadable. "
+                        f"This indicates byte-level splitting instead of page-level splitting. Error: {e}"
+                    )
+
+        finally:
+            # Cleanup
+            for split_file in split_files:
+                if os.path.exists(split_file):
+                    os.remove(split_file)
+
 
 @pytest.mark.unit
 class TestShouldSplitFile: