Compare PDFs

Comparing two PDFs tells you which pages changed between two versions of the same document: a renegotiated contract, a corrected plan, a reprinted brochure, a reviewed report. The tool compares how pages look rather than raw text, so it also spots a replaced image, a shifted table or a changed colour. Both files are analysed in your browser and a report appears straight away.

Each page of both documents is drawn as a low-resolution image (scale 0.55, about 40 dots per inch) and compared with the page with the same number in the other document. A pixel counts as different when the average gap between its red, green and blue components exceeds 24 out of 255, which ignores tiny anti-aliasing variations.

A page is declared different as soon as more than 0.25% of its sampled pixels have changed. Two pages of different sizes, or a page present in only one of the documents, count as entirely different (100%).

The report gives each PDF’s page count, the list of changed pages, the average visual difference — the mean of the percentages of all pages — and whether the documents are visually identical. Pages are compared by position: a page inserted at the start shifts all the following ones, which will then show as changed.