Compare Two PDFs and Highlight the Differences

Runs in this tab, on pdf.js, pdf-lib and Tesseract (WebAssembly), so your file is read from your own device and never sent anywhere. Check it yourself

How to compare two PDFs and highlight the differences

Add the older version first The order decides what counts as added and what as removed, so put the version you already agreed to on the left.

Add the newer version Both files are read in your browser. Contracts and drafts are exactly the documents that shouldn’t go to a comparison server.

Choose what to ignore Ignore capital letters and Ignore punctuation stop “Buyer” versus “buyer” or a straightened quote mark from being reported as changes.

Read every change Additions and removals are highlighted in both versions, and listed with their page numbers so nothing is skimmed past.

Check the numbers by hand A changed figure in a payment schedule is the change that matters most and the easiest to miss in a long list. Read those against the page.

What does a PDF comparison actually check?

The words. Each document’s text is extracted in reading order and the two sequences are matched up, so an inserted clause, a deleted sentence or a changed number is found wherever it falls — even when the edit has pushed everything after it onto the next page.

What it doesn’t see is appearance. A changed logo, a different color or font, or a table restyled without changing its contents isn’t reported. For a contract that is the right trade: the binding part is the text.

How do you read the results?

Text moved from one place to another shows as removed where it was and added where it went, not as a move — so a pair of matching blocks is usually a reshuffle, not a rewrite.

The side-by-side view pairs pages by number. If a page was added or removed, the two sides drift apart from that point, but the highlights and the list of changes stay exact. And if the second file is a rewrite rather than an edit, changes are marked in larger blocks and the result says so.

How do you compare scanned PDFs?

A scan is a picture of words, so there is nothing to compare until the text has been recognized. Run both files through OCR PDF, in the language they are written in, then compare the searchable copies.

Expect a little noise: OCR can read “rn” as “m” or a faint comma as nothing, and those show up as tiny differences. A one-character change in a scanned comparison is worth checking against the page before you raise it with anyone.

When is comparing two PDFs worth doing?

Whenever someone sends a “clean” version and asks you to sign it. The usual cases:

A contract or lease returned without tracked changes after negotiation.
A policy, terms of service or handbook re-issued with “minor updates”.
The final print file checked against the approved draft before it goes to the printer.
A supplier’s new terms against last year’s.
A thesis or report checked against the version your supervisor already read.

Questions

How do I compare two PDF files for differences for free?

Open both in Compare PDFs, older version first. Every added and removed word is highlighted side by side and listed with its page number. Nothing is uploaded.

Can it compare scanned PDFs?

Yes, after OCR. Make both files searchable with OCR PDF first; the comparison then works on the recognized text.

Does it show formatting changes?

No. Only the words are compared, so a changed font, color, picture or layout that leaves the words alone isn’t reported.

Is it safe for confidential contracts?

Both files are read in your browser tab and never uploaded, so no third party sees either version.