PDFs are the standard format for contracts, reports, invoices, and official documents. But when you receive a revised PDF, there's no built-in way to see what changed — you're left reading both versions side by side, hoping you catch every edit.
ChangeChecks solves this by extracting the text from both PDFs and running a word-by-word comparison.
How it works
The tool extracts all text from both documents using Mozilla's pdf.js library — the same technology Firefox uses to display PDFs. It then compares the text word by word, highlighting every difference.
What you'll see
A summary bar at the top tells you how many change regions were found, how many words were added or removed, and how similar the documents are overall. A context line tells you where most changes are concentrated.
Below the summary, the full comparison shows every difference with removed text in coral and added text in sage. You can navigate between changes using the arrow buttons or keyboard shortcuts (J and K).
Important notes about PDF comparison
The comparison focuses on text content. Layout changes — moved images, reformatted tables, changed fonts — won't appear in the comparison because the tool extracts plain text from the PDF structure.
Common use cases
Comparing contract revisions sent by clients or legal teams. Checking policy documents for changes between versions. Verifying that a PDF export matches the source document. Reviewing report updates to see what data or conclusions changed.