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Compare PDF
Spot changes between two versions. Free, no sign-up.
or drop them here
Compare PDF runs inside your browser — your file never reaches our servers.
How to compare two PDFs
Both documents’ text is extracted and compared word by word, and you get a report of the changes.
- Select two PDFs. The old version first, then the new one.
- Compare. Text is extracted from both and diffed word by word.
- Download the report. A Markdown summary of every addition and removal.
What is compared, and what the report says
Both files are opened on your machine and their text pulled out page by page, whitespace-normalised and joined into one stream per document. The two streams are then diffed word by word, a word being whatever sits between spaces — so punctuation travels with the word beside it and "fee." against "fee," counts as a change. Nothing else is examined. Fonts, colour, images, spacing and position are invisible to it: making a sentence bold changes nothing, and moving a paragraph shows up as a removal in one place and the same words added in another.
The download is comparison.md — both filenames with their page counts, the totals for words added, removed and unchanged, then every changed run in order, additions in bold with a plus and removals struck through. Unchanged text is not repeated, so what you get is a list of changes rather than a marked-up copy of the document. Two things catch people out. Running headers, footers and page numbers are part of a page's text, so a version that has repaginated produces a scatter of tiny numeric changes among the real edits. And if neither file has a text layer the tool refuses outright rather than reporting them identical — the worst possible answer to give someone checking a contract against its copy.
How long a document it can take
Finding the longest sequence of words the two documents share is what lets the report distinguish an insertion from a wholesale rewrite, instead of calling everything after the first change different. It costs memory: the comparison builds a table with one cell for every pair of words. Two documents of 10,000 words each — roughly twenty pages of prose apiece — is 100 million cells, around 400 MB while it runs. Two hundred-page reports would need far more than a browser tab will hand over, and the tab runs out of memory rather than finishing.
So compare like with like, in pieces. Cut both versions at the same chapter boundaries with Split PDF, or pull the clause you care about out of each with Extract pages, and compare those. The report is shorter, it finishes, and a change is far easier to place when you already know which section it came from.
Questions
Does it compare layout and images too?
Not yet — this compares the text, which is what matters for contracts, papers and policy documents. Visual comparison of images and layout is a desktop feature.
Can I compare scanned documents?
Run OCR PDF on both first so there is text to compare; otherwise the pages are just images.
Does the report tell me which page a change is on?
No. The documents are compared as one continuous stream of words each, so a change is located by the words around it rather than by a page number. If you need to know where, compare a section at a time — smaller pieces make the position obvious.
Why is a paragraph I only moved reported as both removed and added?
Because the comparison works on the sequence of words the two documents have in common. Text that has moved is no longer part of that sequence, so it is reported as gone from where it was and new where it now is. The wording in both entries will be identical, which is how you recognise a move rather than a rewrite.
Why does it flag text I never touched?
Usually one of two things, both about how a PDF stores text rather than what you wrote. A word broken across a line with a hyphen arrives as two pieces, so it differs from the same word unbroken in the other version. And a page whose text is stored in a different order from the one it displays — common with two columns, sidebars or footnotes — is read in the stored order, so the two files can disagree about sequence without disagreeing about content.
Are my files uploaded to a server?
No. Every tool on this site runs inside your browser, using the same engine as the Folia desktop app. Your file is read from your disk into your browser’s memory, processed there, and handed back as a download. It never crosses the internet, so there is nothing for us to store, leak or hand over.
Is there a file size limit?
We impose none. The only ceiling is your own device’s memory, which differs from one computer to another — so we read what your browser reports about this machine and show the resulting limit on the page. Light tools like merge and rotate handle far more than heavy ones like OCR, which must render every page. For anything larger, Folia for Desktop has no limit at all.
Is it really free? Do I need an account?
Yes, and no. Every tool is free and unlimited, with no watermark and no sign-up. Ads pay for the site, and your own computer does the work, which costs us nothing. Signing in with a paid Folia plan simply removes the ads.