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Compare Two PDFs Free (Spot Differences Online)
Contract v2 or v3? Which invoice did the client actually approve? When two PDFs look almost identical, finding the one changed paragraph by eye is slow and error-prone — and Adobe charges for its compare feature.
PdfWord's Compare PDFs tool does it free, in your browser, with three views: side-by-side for a honest look at both versions, overlay with an opacity slider that makes shifted text shimmer, and diff highlights that paint every changed pixel red and score each page's similarity. No signup, and your documents never leave your device.
Compare Two PDFs in 4 Steps
- Open the Compare PDFs tool — Go to the compare page.
- Upload both files — Drop the original into “PDF A” and the revised version into “PDF B”.
- Pick a view — Side-by-side, Overlay (drag the opacity slider), or Diff highlights for red-marked changes.
- Review the scores — Each page pair shows a similarity percentage; download a diff report PDF if you need proof.
How the Diff Engine Works
Both pages are rendered at identical scale, then every pixel is compared. Pixels whose color channels differ beyond a small threshold are flagged as changed — the threshold ignores anti-aliasing noise so you don't get thousands of phantom differences. Changed regions glow red; identical content fades back.
The similarity score is simply the share of unchanged pixels. A 99.8% page had a typo fixed; a 72% page was heavily rewritten. It's a rendering comparison, not a text comparison — so it catches layout shifts, moved logos, and font changes too.
When PDF Comparison Saves You
- Contracts — verify the signed version matches what you agreed, clause by clause.
- Invoices & quotations — catch quietly changed rates before you pay; generate clean ones with the Invoice Generator.
- Design revisions — confirm the printer's proof matches your file.
- Resumes — check the final PDF matches your edited version before submitting.
Note: it compares the first 20 pages (a speed cap shown in the tool) — for longer documents, split out the section you need first.
Frequently Asked Questions
Both PDFs are rendered page by page and their pixels are compared. Differences are highlighted in red with a per-page similarity score.
Yes — the first 20 pages are compared, which covers the vast majority of real-world documents.
No. Everything renders and compares inside your browser — sensitive contracts never leave your device.
The percentage of pixels that are identical between the two pages. 99%+ means near-identical; lower scores mean heavier edits.