Every PDF I publish — course notes, slides, study guides, reports — carries a digital signature. Nothing shows on the page, but the signature travels inside the file, and it lets you confirm two things about any copy that reaches you:
- It's genuinely mine — signed with my private key, which never leaves my machine.
- It's exactly as I released it — not one byte has changed since. Any later edit, even a re-save, shows up as a broken signature.
Think of it as a signature on a canvas: a small mark that says the work is mine and it left my hands in this state. You never have to check anything — but if you’d like to, here’s how.
Check a document here
Drop any PDF I’ve given you and this page will read its signature — entirely in your browser.
The file never leaves your device — nothing is uploaded.
The signing certificate
The check above already knows my certificate. To verify a document yourself — in Acrobat, on the command line, or on a machine that’s offline — download it here:
anshid-cert.pem anshid-cert.cer (DER, for Acrobat)
| Subject | CN = Anshid Aboobacker, emailAddress = anshidaboobackerk@gmail.com |
| Valid | 2026-09-03 → 2036-08-31 |
| SHA-256 | 7D:21:C7:F4:80:90:7C:76:95:FD:3F:4C:E2:88:B8:5D:EC:A9:B9:C5:66:32:E4:B3:74:BD:B0:8A:DB:12:BF:1E |
| SHA-1 | 72:43:E1:E2:89:60:A0:33:92:B1:BB:73:7B:B5:68:09:8B:07:88:1F |
The certificate is self-signed — it doesn’t chain to a commercial authority, so a PDF reader will mark the signature “valid, signer not verified” until you tell it once to trust this certificate. That’s a one-time setup step. Match the SHA-256 fingerprint above against what your reader shows before you add the trust.
Verifying it yourself
Adobe Acrobat / Reader
- Open the PDF. The banner at the top shows the document is signed.
- Open the Signature Panel → expand the signature → Signature Details → Certificate Details. Compare the SHA-256 fingerprint with the value above.
- To have it show as trusted from then on: Certificate Details → Trust
→ Add to Trusted Certificates. (Or import
anshid-cert.cerunder Preferences → Signatures → Identities & Trusted Certificates.)
Command line — pyHanko
pip install pyhanko-cli # or: uv tool install pyhanko-cli
pyhanko sign validate --trust anshid-cert.pem document.pdf
A good result reports the signature INTACT, TRUSTED, UNTOUCHED — the signature covers the whole file and the certificate matches.
Command line — poppler
pdfsig document.pdf
Lists each signature, the signer, and whether it covers the entire file. (It won’t say “trusted” unless the certificate is in your system store, but it confirms the signature is cryptographically intact and covers the whole file.)
Questions about a specific document? Email me.