Drop the original in the first box and the changed version in the second, then open the workspace. PDF.js reads the text of both, and by default the whole document is lined up at once, so an inserted page does not throw off everything after it. The pages show removed lines in red on the original and added lines in green on the changed file, and the list of changes names the page of each in both files. Download the report as a PDF if you want a record.
The list compares words, not appearance. A moved logo or a font change does not appear in it; the Overlay and Differences views show those as coloured pixels. Both files need real text for the list; scans need OCR first.
Contract revisions, policy updates, two drafts of the same report, a resend that is supposedly identical. In every case the question is the same and the honest answer is hard to get by eye: what wording changed? Reading both versions side by side finds most of it. A diff finds all of it, and finds it in seconds, which is why programmers have relied on the technique for fifty years.
How to compare two PDFs
Put the older file first
The first box is the original, the second is the changed version. Swapping them reverses every colour, which reads backwards.
Add both PDFs
Drop or browse for each. Both are read into browser memory; neither is uploaded.
Press Compare in the workspace
The text of every page is extracted and lined up across the whole document, so a page inserted or removed early does not shift the rest. The Alignment switch in the side panel changes this to page by page, page 1 against page 1 and so on.
Read the changes, download if needed
Each change in the list names its page in both files; click one to jump to it on the pages. Download report saves the list as a PDF for a record.
A reworded line shows as one changed entry, old and new together, with the differing words marked.
An inserted or removed page shows as added or removed lines, and the rest still lines up. Page by page is the other setting.
Two confidential drafts never leave your machine.
How to read the comparison
- Red mark on the original pageIn the original, gone from the changed version
- Green mark on the changed pageIn the changed version, absent from the original
- A changed entry in the listThe same line, reworded, with the differing words marked
- A label such as A p.3 → B p.4Where that line sits in each file
- No changes listedThe text of the two files is identical
The list holds only differences, so a forty-page contract with two changed clauses produces a handful of entries. The downloaded report works the same way: pages whose text is identical do not appear in it, so you read what changed and nothing else.
What it compares, and what it does not
Any change to the words
- Reworded clauses, changed figures, altered dates
- Added or deleted sentences and paragraphs
- Renamed parties, changed addresses
- Extra or missing pages
- A resend that is not actually identical
Changes that leave the text the same
- A moved logo, a resized image, a new page background
- Font, colour and layout changes
- A line that only moved to another page, in Whole document alignment
- Changes inside images or scanned pages
- Form field values that were not part of the page text
For legal documents, policies and anything text-heavy, the wording is what matters, and the wording is what this surfaces. For a designed brochure where only the layout changed, the list will be empty and be right to. Switch the top bar to Overlay or Differences to see those changes as coloured pixels.
Getting an accurate comparison
- Compare versions of the same document. Two unrelated files produce a long list of differences that means nothing. The tool shines when one file is a revision of the other.
- Both need a text layer. Select a word in each file. If it highlights, there is text. If not, run that file through OCR first, then compare.
- Pick the alignment that fits. Whole document, the default, copes with a page inserted early. Page by page judges each page on its own, and it fills with noise once the page numbers no longer line up.
- Expect rewrap noise. If an edit early in a paragraph changes where its lines break, the lines after it show as changed although their words did not. In Page by page alignment, a paragraph that moved across a page break also shows as removed from one page and added to the next.
- Very long documents are matched more loosely. When the line counts of the two files multiplied pass six million, about 2,450 lines each, the tool stops lining up the order and counts a line as unchanged if the same text appears anywhere in the other file.
Where a diff earns its place
- Contract revisions. Confirm the counterparty changed the dates and nothing else, in the time it takes to scroll a short report.
- Policy and terms updates. See precisely what a new version of a policy adds or removes before agreeing to it.
- Editing drafts. Check that only the intended edits went in and that a paragraph did not vanish in a bad paste.
- Verifying a resend. "Same file as before" is a claim. A diff with no entries is a fact.
Why both files stay in your browser
Comparing two files with an online tool means uploading both, which for a contract negotiation is two confidential drafts leaving your control at once, on a server the other side has never heard of. The comparison is a text operation any browser can perform, so there is no reason to accept that.
The tool is right above
Everything on this page runs in your browser. Scroll up, drop the file, and keep it on your machine.
Common questions
What people ask with the report on screen.
01What does the tool compare?
The text of the two PDFs, line by line. The list of changes shows which lines were removed, added or changed, with the changed words marked, and the Side by side view paints them on the pages. The Overlay view, in the top bar, draws both pages on top of each other and colours anything that exists in only one version, which catches layout and image changes.
02Does it work on scanned PDFs?
Only if both have a text layer. Run each scan through OCR first, then compare the OCR'd files.
03Can I download the comparison?
Yes. Download report saves a PDF that lists every removed and added line with its page, names the alignment used, and shortens very long lines with an ellipsis. Keep it for a record or share it.
04How are pages matched up?
Two ways, set by the Alignment switch in the side panel. Whole document, the default, lines up the text of both files from start to finish, so a page inserted or removed early shows as added or removed lines and everything after it still matches. Page by page compares page 1 with page 1, page 2 with page 2, and so on; if one file has more pages, the extra pages are reported as wholly added or removed.
05Why does a paragraph show as both removed and added?
Usually it was reworded, and the old and new lines sit together as one changed entry. It can also mean an edit changed where the paragraph's lines break, so lines whose words did not change still differ. In Page by page alignment, a paragraph that moved across a page break shows this way too, with its words unchanged.
06Does it show layout or image changes?
Yes, in the Overlay view, chosen in the top bar. Both pages are drawn on top of each other: red pixels exist only in the original, green only in the changed file, and the Differences view fades everything the two share to light grey. Each page is labelled with the share of its pixels that differs. The list of changes covers the words; use both when a file was reformatted as well as edited.
07Are my files uploaded anywhere?
No. Both files are read and compared in your browser, and the report is generated there too.
08Is it free?
Free. Every tool, unlimited use, no signup.