Compare two PDF files

The practical question when someone returns a document is narrow: what is different from the version I sent. Reading both copies side by side to answer it is slow and unreliable, and the changes that matter are exactly the ones easiest to miss.

This tool answers that question directly. It reads the text layer of both files, reconstructs the lines from the position of the text on each page, and marks every line that was added or removed. The counts come first, because the first thing you usually want to know is whether anything changed at all.

Line reconstruction is the part that decides whether the result is useful. A PDF stores glyphs at coordinates, not lines, so text has to be grouped back into lines before it can be compared. Comparing whole pages instead reports a page as changed the moment one word moves, which tells you nothing. Grouping into lines puts each difference next to the sentence it happened in.

Two limits stated plainly. Only text is compared, so two files can match here and still differ in fonts, images, or metadata, and the result says exactly that rather than implying a complete match. And the comparison needs a text layer, so scans of paper need OCR run over them first.

Both documents stay on your device. That matters more for this tool than for most, because the pair being compared is usually a contract, an agreement, or a draft that came back from someone else, and the reason for checking it is often that you do not fully trust the change.