PDF Compare
Upload two PDF files to compare them side by side. Changed lines highlight automatically — pink for removed, green for added. Nothing is uploaded to any server.
Original PDF (left)
Drop or click to browse
Modified PDF (right)
Drop or click to browse
Comparing…
How to Use PDF Compare
Upload the original PDF on the left and the modified PDF on the right by clicking or dragging. Both files are loaded in your browser — nothing is sent to any server. Once both are ready, the tool renders them side by side and automatically highlights differences.
Lines that exist in the left PDF but not in the right are shaded pink. Lines that exist in the right but not in the left are shaded green. Unchanged lines have no highlighting. Drag the vertical divider to resize the panels. Toggle Scroll Sync to keep both panels in step as you scroll through long documents.
Frequently Asked Questions
How does the comparison work? expand_more
PDF.js extracts the text content and positions from each page of both documents. The text lines are grouped by their vertical position and compared using a Longest Common Subsequence (LCS) algorithm — the same principle used by code diff tools. Lines that are not in the common sequence are highlighted.
Can it compare scanned or image-based PDFs? expand_more
No. Scanned PDFs contain images rather than selectable text. The tool can only highlight differences in text-based PDFs where the text can be extracted.
Does the comparison work across different page counts? expand_more
Yes. If the two PDFs have different numbers of pages, the tool compares matching page numbers where both exist and renders any extra pages without highlighting.
Are my files uploaded to a server? expand_more
No. Both PDFs are processed entirely in your browser. No data leaves your device.
What do the colours mean? expand_more
Pink highlights on the left panel indicate lines present in the original (left) PDF that are missing or changed in the modified (right) PDF. Green highlights on the right panel indicate lines that are new or changed in the modified version.
Can I compare PDFs with different layouts or document types? expand_more
Yes, but the results will show many differences since the text content differs. The tool is most useful for comparing two versions of the same document — contracts, reports, or forms where only a few sections changed.