How to Compare Two PDF Files for Changes

What a text diff actually compares

PDF Compare reads the embedded text layer of each PDF — the words a PDF editor actually stored on the page — and checks them line by line against the original you select. Lines found only in the original are marked removed (red); lines found only in the revised file are marked added (green). Everything is matched page by page, on the shortest shared page count.

Because the comparison is text-based, it is not a visual diff. A paragraph that changed font or color, an image that was swapped, a margin that was nudged, or a table's gridlines are not reported unless their words changed too. Scanned pages have no text layer at all, so they compare as empty and unchanged. That is by design: the tool only claims to compare words, not pixels.

Add the files and pick the original

Use Add PDF to choose two to five PDFs, up to 100 MB and 200 pages each. The first file you add becomes the original, but you can select Original on any file in the list before comparing. Every other file is then compared against it.

Encrypted or password-protected PDFs are rejected the moment you add them — unlock such files with PDF Unlock first. A file that is not a real PDF, or one with more than 200 pages, is also rejected up front so you are never left wondering why comparison failed.

Compare and read the results

Click Compare PDFs. Each revised file gets its own result card with a page-by-page view. Green lines are additions, red lines are removals, and unchanged lines stay neutral. Flip the page numbers to move through the document, turn on Only show changed lines to skip the noise, and use the ignore-case or ignore-whitespace options when drafts differ only in capitals or spacing.

Reordered text is reported as removed plus added: line matching is position-aware, so a paragraph that moved pages shows up as a removal on one page and an addition on another. If one file has more pages than the other, only the shortest shared page count is compared, and the tool says so.

Download the report and check the rest

Download diff report (.txt) saves every change against every revised file, named after the original, for sharing or an audit trail. Because covers and empty pages can shift matches, skim the marked lines before relying on them, and re-check anything the comparison cannot see — images, fonts and layout — visually in the two PDFs.