Compare PDF

The tool reads the words on every page of both PDFs, together with their positions, and compares the whole documents in one pass using a proven diff algorithm (the same family of algorithms used by software developers to compare code). Comparing the whole document — rather than page 1 with page 1 — matters: when one paragraph is inserted on page 2, everything after it shifts, and a page-by-page comparison would flag the rest of the document as changed.

The results are grouped into readable changes: added text in green, removed text in red, changed wording shown as both, and passages that were moved elsewhere in purple instead of being reported as a deletion plus an insertion. Images that were added, removed, moved or resized are reported too. Tick "Ignore case" or "Ignore punctuation" to hide trivial edits.

Some changes aren't words: a revised floor plan, a different logo, an added signature or stamp, a corrected chart, or any change on a scanned page. Visual mode renders both versions and compares them pixel by pixel. The overlay shows content that only exists in the original in red, new content in green, and recoloured content in blue. Raise the sensitivity to catch faint changes, lower it to ignore scanner noise, and keep "Align scans" on when two scans were fed through the scanner at slightly different positions.

Redlines aren't always trustworthy — a counterparty might send a clean PDF without tracked changes, or a change might slip in outside the marked-up sections. Comparing the PDF you sent with the PDF you received shows every edit regardless of how the file was made. The downloadable report lists each change with page numbers and keeps both versions of each page with the edits marked, which makes it easy to share with a colleague or keep for your records.

Architects, engineers and print shops often receive revised drawings or proofs with only a vague note about what was updated. Visual comparison pinpoints moved walls, changed dimensions, shifted logos and colour changes, while text comparison checks specifications and captions. Because pages are matched by content, an inserted sheet doesn't throw off the rest of the set.

• Put the older file on the left (Original) and the newer one on the right (Revised), or use Swap.
• Use Text mode for documents created on a computer — it is precise to the word.
• Use Visual mode for scans, drawings and anything where layout matters.
• Step through changes with the arrow buttons; clicking a highlight selects it in the list.
• For very long documents, keep "Only pages with changes" on so the report stays short.