PDFTrust

How to prove a PDF has not been changed: verification stamps explained

Certificates, invoices and signed letters get edited and forwarded. Learn how a QR verification stamp lets anyone check that a PDF is exactly the one you issued.

· 6 min read

Once a PDF leaves your hands, it can be edited in seconds: a different amount on an invoice, another name on a certificate, a changed date in a letter. The receiver usually has no easy way to tell. A verification stamp solves this by giving every document a fingerprint that anyone can check.

What a verification stamp is

When you stamp a PDF with Verify Stamp, DocuTools adds a small QR code and a unique code such as K7QX-M2PA to the page. It then records the SHA-256 fingerprint of the finished file. The fingerprint is a short string that changes completely if even one byte of the file changes. We store the fingerprint and the code, never the file itself.

How someone checks your document

  1. They scan the QR code or open docutools.net/verify.
  2. They choose the PDF they received. Their browser calculates its fingerprint locally; the file is not uploaded.
  3. If the fingerprint matches our record, they see "Authentic" with the stamp date and page count. If anything was changed, re-saved or replaced, the check fails.
Stamp your first documentVerify Stamp

Good uses for verification stamps

  • Certificates for courses, events and training.
  • Invoices and quotes you send to clients.
  • Official letters, reference letters and HR documents.
  • Reports where the numbers must not be altered after delivery.

What a stamp does and does not prove

A matching stamp proves that the file is identical to the one stamped, and when it was stamped. It does not prove who wrote it, that its content is true, or that it is legally binding. Think of it as a tamper-evident seal, not a notary. If a stamp is misused you can revoke it from your dashboard, and checks will show it as revoked.

Tips

  • Stamp the final version. Any edit afterwards, even re-saving in another app, breaks the match.
  • Stamp only the last page if you do not want the QR code on every page.
  • Combine it with a workflow: merge, number pages, then stamp as the last step.

Verify Stamp requires an account with a verified email address, so every stamp has an accountable issuer.