How does the comparison work?

Both files are opened into the editor's document model on your device. Paragraphs are aligned first — identical ones matched, edited ones paired by similarity, identical text that moved recognised as a move — then each pair is compared word by word, with formatting differences noted. The result is the revised document with every difference as a tracked change, the same shape Word's Compare produces.

Can I accept or reject the differences?

Yes. Open the result in the Word Editor: every difference is a tracked change with the reviewing pane, next/previous, accept and reject, and it saves back to .docx with the changes intact.

What does Combine do?

Combine takes the original plus two reviewers' copies and merges both sets of edits into one document, each change under its reviewer's name — Word's Combine, on the model.

Is anything uploaded?

No. The diff runs in a Web Worker in your browser; the files never leave the device.

Is this the same as the PDF compare tool?

No. PDF compare works on rendered pages and text layers; this tool works on the document model, so it knows about paragraphs, formatting and moves and produces tracked changes rather than a picture.

Compare Documents — Every Difference as a Tracked Change, Free

Compare two versions of a Word, ODT, RTF, Markdown or HTML document and get every difference as tracked changes, word by word with formatting and moved paragraphs, plus a side-by-side view. Combine two reviewers' copies. Nothing is uploaded.