What it does
When someone sends back “the final version”, this tool shows exactly what is different from the one you sent. It compares word by word, so a changed number or a deleted “not” stands out. New words are underlined in green and removed words are struck through in red, like a lawyer’s redline.
Add a PDF, a Word file or a text file on each side, or paste text. Everything stays in your browser, so it is fine for contracts and offers. Before you send your own version out, run pre-send check; to turn a file into another format first, use file converter.
How to use it
- Put the older version under Original and the newer one under New version. A file fills the text box, and you can still edit it.
- Press Compare. The count tells you how many separate changes there are, plus words added and removed.
- Switch between one column and side by side.
- Press Download redline PDF to save the marked-up result, or Print to print it or save it as a PDF from your browser.
What each setting does
- Ignore capital letters: “Agreement” and “agreement” count as the same word.
- One column: shows removed and added words together in reading order.
- Side by side: the original on the left with removals, the new version on the right with additions.
Worked example
Original: “The cat sat on the mat”. New: “The dog sat on the red mat”. The result shows 2 changes: “cat” replaced by “dog” (one change) and “red” added (another). That is 2 words added and 1 removed.
FAQs
Does it compare layout, fonts or pictures? No. It compares the words only.
Why do I see odd breaks from a PDF? PDFs do not store paragraphs, so line breaks are guessed. They never count as changes; only words do.
Can it read scanned PDFs? No. A scan is a picture. The text has to be real text.
Tracked changes in a Word file? Deleted text is left out and inserted text is included, so you compare the document as it would read if accepted.
Is my file uploaded? No. Everything runs in your browser.
Where the numbers come from
- Word-level comparison uses the Myers shortest-edit method written for fibub. Word files are read with fflate, PDFs with PDF.js and pdf-lib. All open source.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.