Does either document get uploaded?

No. The comparison runs in a Web Worker in your own browser. For contracts that matters more than for most jobs: the documents people redline are precisely the ones under an NDA, and uploading them to a free tool is often a breach of the agreement being redlined.

Does it detect moved text, or just deletions and insertions?

It detects moves and marks them as moves, with the moved-from and moved-to positions paired, which is what stops a relocated clause looking like a deletion and an unrelated insertion at opposite ends of the document.

What about formatting-only changes?

They are marked as formatting changes rather than as edits to the text — the case where somebody changed a defined term from bold to italic, or quietly changed an indent so a sub-clause now reads as a clause.

Can I compare a PDF against a Word file?

Not directly and not reliably. A PDF has no paragraph structure to align, only positioned text. Convert the PDF to a document first and expect the reconstruction to introduce differences of its own, which is why the comparison that matters should be between the two editable originals.

Is the redline a real document I can send?

Yes. The result is a document with real tracked changes, so it saves as a .docx that opens in Word with the revisions intact, and everyone can accept or reject them in the tool they already use.

Compare Two Versions of a Contract

Two drafts and no idea what moved. Produce a redline in your browser: every insertion, deletion and moved clause as a tracked change, with neither file uploaded.