Comparing two PDFs reliably takes two passes. First, compare the words, numbers, tables, and page appearance. Then compare the files' properties. The first pass tells you what a reader sees; the second can expose a changed export, missing page, different producer, encryption change, or other structural difference.
PDFCheck handles the second pass. It does not claim to highlight every changed word or pixel. For contracts and other consequential documents, use a trusted content-comparison tool or careful side-by-side review as well.
Both files are uploaded over HTTPS for server-side comparison. The original uploads are not retained after the request; the comparison result is stored according to the retention terms in the Privacy Policy.
What PDFCheck Compares
The PDF comparer extracts a fixed set of properties from each file and places them side by side:
- Basic file facts: filename, file size, page count, and PDF version.
- Document properties: title, author, subject, creator, producer, creation date, and modification date.
- Structural signals: encryption, tagged status, font count, image count, and the presence of JavaScript.
A difference is a prompt to investigate, not proof of tampering. A normal re-export can change the producer, dates, size, fonts, or internal structure without changing the visible meaning.
A Practical Two-Pass Workflow
1. Confirm which file is the reference
Name the files clearly and record where each came from. Keep the originals unchanged.
2. Compare visible content
Review wording, figures, tables, footnotes, page order, headers, and attachments. For long documents, use a dedicated text or visual diff that supports your file type.
3. Compare PDF properties
Open the PDF comparer, upload both files, and review every property marked as different.
4. Explain each important difference
A page-count change may mean pages were added or removed. A producer change may mean the document was exported by another application. Encryption or JavaScript changes deserve separate security review.
5. Verify the final file
Open it in the recipient's normal reader, check signatures in an approved trust workflow, and validate the exact copy you plan to send.
What a Property Difference Can and Cannot Tell You
| Difference | Useful question | Do not assume |
|---|---|---|
| Page count | Were pages intentionally added or removed? | Which words changed |
| Creator or Producer | Was the file re-exported by another application? | Who edited it |
| Creation or modification date | Does the timestamp fit the known workflow? | That the timestamp is trustworthy |
| Encryption or JavaScript | Did the security profile change? | That the file is safe or malicious |
Scans, Signatures, and Re-exports
An image-only scan has little searchable text, so content comparison may require OCR. OCR can introduce recognition errors; verify names, dates, amounts, and clause numbers against the page image.
A digital signature serves a different purpose. A trusted PDF reader can evaluate whether signed byte ranges changed and whether a certificate is trusted. It does not explain every difference between two drafts. Read the signature verification guide before relying on a signed file.
If one version was printed and scanned, or exported through another application, many properties may differ even when the visible content looks similar. Treat those signals as leads for review.
Sources
Bottom line: compare visible content and file properties separately. PDFCheck makes the property check fast; it does not replace a content diff or professional review.