How to Compare Two PDF Files and See Every Text Change, Page by Page
A contract comes back “with a couple of small fixes”. A supplier reissues an invoice. In each case you hold two versions of one document and one question: what changed? This guide shows how to compare two PDF files for free, what a PDF compare really checks, how to read the PDF diff it produces, and how to fix the two results that fool people most — “no differences” on files that clearly differ, and “every page changed” when only one did.
1. What a PDF Compare Actually Checks
A PDF exported from a word processor or generated by accounting software carries a text layer: the characters you can select, search and copy. When you compare PDF files here, that text layer is what gets compared. Each page is read back into lines, top to bottom, and page 1 of the original is set against page 1 of the revision, page 2 against page 2, and so on.
That makes it the right tool to compare PDF documents for differences in wording: a changed clause, a deleted paragraph, a different figure, a date that moved. Think of it as a PDF diff checker that accepts the PDFs themselves.
Images, logos, colours, fonts, bold or italic styling and layout are not compared, and neither are comments, annotations, form field values or signatures. How text is stored in a PDF is defined in ISO 32000-2, the PDF specification; a file only has comparable text if whatever created it wrote that text in.
2. How to Compare Two PDF Files for Differences
Here is how to compare two PDF files for differences with the tool above — a way to compare PDF online free, with no account and no paid tier. It is also how to compare two PDF documents without paid PDF software: no licence and no trial.
- Drop the original into “Original (A)”. The older version, the one you already agreed to.
- Drop the revision into “Revised (B)”. The two drop zones sit side by side, so it is clear which file is which.
- Set the two options. Ignore whitespace differences is on by default and should usually stay on, so a re-export that shifts spacing does not flood the results. Ignore case is off by default; switch it on only when capitalisation changes do not matter to you.
- Press Compare. The results appear below the button.
The same four steps answer how to find changes in a revised PDF when nobody marked them, and how to compare PDF versions redline free of paid legal software.
3. Reading the PDF Diff: Pages, Redline, Metadata, Patch
The results come in five parts.
- The stats strip shows the page count and file size of A and B.
- The verdict counts pages that differ and lines removed and added, or states that the text is identical.
- The metadata table sets title, author, subject, creator, producer and both dates side by side, differences in red.
- One card per changed page. Removed lines carry a minus sign, added lines a plus sign, and where a line was edited, the changed words are highlighted inside it. Unchanged pages are left out, so one edit produces one card.
- A unified diff of the text, with Copy and Download buttons.
That last part is how you export PDF differences as text (diff patch format). The download is a plain-text file named pdf-diff.patch, with each block labelled by page (“A page 3” against “B page 3”), in the unified diff format developers already read. It is the only export: there is no annotated PDF or highlighted comparison report, and none of our other tools produces one. If you need a record to send to someone, attach the patch file, or copy the changed lines from the page cards into your reply or a cover note.
The metadata table is the quickest answer to how to see who created or modified a PDF. Creator is the application the document was written in and Producer the software that wrote the PDF. When you compare PDF metadata, author, producer and dates, a new Producer or later modification date shows a file was re-saved, even when the text matches. Treat these fields as a hint, not proof: any editor can rewrite them. Only fields that at least one file fills in appear in the table, and the Keywords field is not compared.
4. PDF Compare Showing No Differences? The Fix
The most dangerous result is a PDF compare showing no differences on files you can see differ. It almost always means they are scans: pictures of text with no text layer. Both sides come out empty, and two empty documents match.
To test, try to select or search for a word in the PDF. If you cannot, there is no text layer. To compare scanned PDF documents, run both files through the PDF OCR tool first, then compare the two outputs. Expect a few stray character differences on poor scans.
The other blocker is a lock. To compare password protected PDF files, remove the protection first — the tool refuses encrypted files. If you know the password, use PDF Unlock to save an unlocked copy, then compare that copy.
“Identical” means identical text. A matching verdict is reliable for wording, so it confirms a reprint says the same thing. It says nothing about a changed logo, stamp, signature or form field.
5. PDF Compare Shows Every Page Changed? Line the Pages Up
The opposite surprise: you expected one edit and the PDF compare shows every page changed from page 6 onwards. Pages are matched by number, so when the revision gained or lost a page, everything after it sits one page off.
Check the page counts in the stats strip. If they differ, line the files up first: delete the extra page from a working copy with the PDF page remover, or pull matching ranges out of both files with extract pages from PDF and compare section by section.
Multi-column layouts can also read back in a slightly different order, and an early edit can push lines onto the next page. Both show as lines removed and re-added nearby; the highlighted words show what really changed.
6. Contracts, Thesis Drafts and Invoices: Worked Examples
Contract version 1 against version 2. When you compare two versions of a contract PDF, put the copy you agreed to in A and the counterparty’s return in B, with Ignore case off. Read every page card: the point is to catch the edit nobody mentioned.
Thesis drafts. To compare thesis drafts, PDF exports should use the same template so page breaks match; otherwise compare chapter by chapter.
A reissued invoice. When you compare two invoices, PDF differences show up as single highlighted words: a changed amount, due date or reference. If the text is identical but the modification date differs, the invoice was most likely just regenerated.
One PDF and one Word file. To text compare PDF and Word versions, both sides must be the same format. Turn the Word file into a PDF with DOCX to PDF and compare here, or convert the PDF with PDF to Word. For plain text, the diff checker is quicker.
On any computer. You can compare two PDF files on Mac, Windows or Linux, and compare PDF files on Chromebook, the same way.
7. Why Use Cortexis as Your Free PDF Comparison Tool
Most pages offering a PDF comparison tool are a drop zone and a promise. If you want a free PDF compare tool as an alternative to paid PDF software for comparing files, here is what this one does.
Free, with no account
No sign-up, no trial and no paywall in front of the results.
Word-level highlights
Edited lines show the exact words removed or added, so one altered figure stands out.
Metadata compared too
Author, creator, producer and dates side by side, to show which version is which.
A patch you can keep
Download the unified diff as pdf-diff.patch, labelled page by page.
Your documents stay private
Files are never stored on our servers and nothing is retained after your session.
Nothing is used for training
Your documents are never used to train any model.
It compares two files at a time, text only, with no visual overlay. It is one of our free document tools on the same terms.
8. Frequently Asked Questions (FAQ)
How do I compare two PDF files for free?
Drop the original into Original (A) and the revision into Revised (B), then press Compare. You get the changed pages with highlighted words, a metadata comparison and a downloadable patch.
How to check if two PDFs are identical?
Compare them with Ignore whitespace on. If the verdict says the text is identical, the wording matches on every page. Images, stamps and signatures are not checked.
Can I compare PDF side by side?
The two files load side by side as A and B. The result is one redline view per changed page, with removed and added lines marked, which is quicker to scan than two full pages.
Why does the comparison say there are no differences when the files clearly differ?
The files are almost certainly scans with no text layer. Run both through the PDF OCR tool, then compare the results.
Can it compare images, layout or formatting?
No. Only the text on each page is compared, so changes to images, fonts, styling, layout, annotations and signatures are not detected. None of our tools does a visual comparison.
Is it safe to put contracts into online PDF tools?
It depends on what the tool keeps, so check its privacy terms before adding a confidential contract. Here, files are never stored on our servers, nothing is retained after your session, and nothing is used for training. No account is needed, so the comparison is not tied to your name either.
Can I download the comparison as a highlighted PDF?
No. The only export is a plain-text unified diff named pdf-diff.patch, and none of our tools produces a marked-up PDF. For a visual record, screenshot the page cards.
Can I compare more than two PDFs at once?
No. Each comparison is one original against one revision. For several drafts, compare each with the next in turn.
Next, check the outline with the PDF bookmarks tool, hide sensitive text with PDF redaction, sign the agreed version with PDF eSign, or combine the final papers with the PDF merger. To learn to build tools like this, our free full-stack web development course covers the groundwork.