Prove a document hasn't been altered
A SHA-256 hash is a 64-character fingerprint computed from the file's content. If anyone changes a single comma, the fingerprint changes completely. That's why it's used to verify the integrity of electronic case files, evidence and contracts.
The fingerprint is computed in your browser. The certificate can be a separate PDF (recommended, so the original stays unchanged) or appended as the last page. It proves integrity, not the author's identity.
How to calculate a SHA-256 hash, step by step
- 1
Select the PDF.
- 2
Enter the issuing office or person, choose the purpose and how to deliver the certificate.
- 3
Download the certificate with the SHA-256 fingerprint.
Frequently asked questions
How do I later check that the file hasn't changed?
Compute the SHA-256 of the same file again (here, with certutil -hashfile file.pdf SHA256 on Windows, or shasum -a 256 file.pdf on Mac) and compare it with the certificate.
Why is a separate certificate recommended?
If you append the certificate to the PDF, the resulting file is different and has another fingerprint. With a separate certificate, the original remains verifiable.
Is this the same as a digital signature?
No. The hash proves the file hasn't changed, but it doesn't identify who signed it.