Compare Two PDFs

1. 1Add the original document on the left and the revised copy on the right.
2. 2Press Compare — both files are read page by page.
3. 3Look through the pages that changed; added lines are marked with a plus, removed lines with a minus and a strike-through.
4. 4Download the comparison as a text file if you need to send it on.

The text of each page is extracted from both documents, then matched with a longest-common-subsequence comparison — the same approach source-control tools use. That finds the smallest set of additions and deletions turning one version into the other, so a paragraph inserted at the top does not make every line after it look changed.

Pages are compared in order, and pages with no differences are left out of the report so that what remains is only what matters. When the two documents have different page counts that is called out, because everything after an inserted page will legitimately appear changed.

Only the words are compared. Images, fonts, colours and layout are not, so a document that was reformatted without editing the wording correctly reports no text differences. Additions and removals are marked with symbols and a strike-through as well as a background, so the report is readable without relying on colour.

The file is read into your browser's memory, changed there, and handed straight back to you. Nothing is uploaded, so there is no queue and no copy sitting on a server afterwards.

• Compare text-based PDFs. A scan has no text to compare, so run it through OCR first if you must.
• Use it before signing a revised contract to see exactly which wording changed between versions.
• If the page counts differ, everything after an inserted page will legitimately appear changed — start reading from the first difference.
• Layout, fonts and pictures are not compared, so a reformatted document with the same wording shows no differences.

• How to compare two versions of a PDF and see exactly what changed