Compare two PDFs and highlight what changed
Upload two PDFs and get a comparison report that visually highlights every difference between them — text edits, layout shifts, image swaps, even subtle stamp moves. Perfect for contract reviews, redline checks, and document audits.
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Comparing two versions of a PDF — a contract draft and the redline you got back, an old and new version of a marketing brief, last year's policy document and this year's — is one of the most painful manual tasks people do with PDFs. Word's Track Changes only works for documents authored in Word; signed PDFs or scanned ones are opaque. PDFOnly's Compare PDF tool runs a true visual diff: every page of both files is rendered to an image, the images are subtracted pixel-by-pixel, and any region that changed is flagged. The output is a PDF report you can share, archive, or attach to your review notes.
How to compare pdf step by step
- 1
Upload both PDFs in order
Drop the original file first, then the revised file. Order matters because the report labels them as 'A' (original) and 'B' (revised) throughout.
- 2
We render and diff every page
Both PDFs are rasterized at 100 DPI using Ghostscript. Each page-pair is compared pixel-by-pixel. Pages that exist in only one file are flagged as added or deleted. Pages that exist in both but differ visually are marked as 'changed'.
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Download the comparison report
The output is a single PDF with a summary header showing total pages compared and how many changed. Then for every changed page, you get the original page (left) next to the revised page (right) with the changed regions highlighted in red.
Why compare pdf on PDFOnly
True visual diff, not text-only
Most online comparison tools only diff extracted text — they miss image changes, layout shifts, font swaps, signature placements. We compare actual rendered pixels.
Works on signed and scanned PDFs
Text-extraction comparison fails on signed documents and scanned forms because the text is locked or absent. Pixel-level diffing works on anything that renders.
Self-contained output
The report is a regular PDF. Email it, archive it, drop it in your DMS — no proprietary format, no special viewer required.
Privacy by default
Both files are deleted within an hour of processing. We don't keep contract drafts or sensitive documents around longer than the job requires.
What people use compare pdf for
A few common scenarios. If your workflow looks like one of these, this tool is a good fit.
Contract redline review
Counsel sends back a redlined version of your contract. Compare PDF flags every changed clause page-by-page so you can verify their edits match what was negotiated, before you sign.
Policy or compliance document audit
HR pushes a new version of the employee handbook. Run Compare PDF on the old and new versions to catch every wording change — useful for compliance archives and change logs.
Marketing collateral version check
Designers send back a 'v3 final' PDF after rounds of edits. Use Compare PDF to verify all the agreed-upon changes are reflected and nothing else slipped in.
Academic paper revisions
Co-authors send revised drafts. Compare PDF shows you exactly which pages changed without forcing you to re-read the entire paper.
What you get
- Visual pixel-level diff catches edits that text-only tools miss
- Detects added pages, deleted pages, reordered pages, and visual changes
- Works on any PDF — including scanned, image-based, and signed documents
- Output is a self-contained PDF report you can share or archive
- Files auto-deleted in 1 hour — your contracts stay private
- Free up to 100 MB per file (200 MB on Pro)
Frequently asked questions
What kind of differences does it detect?
Anything that changes the visual rendering of a page: added/removed text, font changes, image swaps, layout shifts, signature placements, watermark additions, color changes — all of it. If a human eye could see the difference, the tool catches it.
What if the two PDFs have different page counts?
We compare overlapping pages. Pages that exist only in the longer document are flagged in the report as 'added' (or 'removed' depending on which was longer). You can still see what's in those pages — the report includes them.
Will tiny rendering differences (anti-aliasing) cause false positives?
We use a small tolerance threshold so sub-pixel anti-aliasing differences don't trigger flags. Only meaningful changes — text edits, layout shifts, image swaps — show up in the report.
Can I compare a scanned PDF with a typed one?
Yes — but every page will likely be flagged as 'different' because the rendering of typed text vs. scanned text isn't pixel-similar. The tool works best when both PDFs have similar provenance (both scanned, or both typed).
Does the order of upload matter?
Yes — the first file you upload is treated as 'A' (original), the second as 'B' (revised). The report's labels and the diff direction depend on this order. If you reverse them, the highlights look inverted.
How big can the PDFs be?
Up to 100 MB each on the free tier (200 MB on Pro). Very long PDFs (200+ pages) take proportionally longer to process — we have to render every page of both documents.
Is this safe for confidential contracts?
Files are auto-deleted within an hour, transmitted over HTTPS, and never used to train AI. Self-host if you need air-gapped processing — the source code is straightforward.
Ready to compare pdf?
Free to use for the basics. Files are auto-deleted within an hour and never used to train AI.
Open Compare PDF