What if the PDF shows Validity unknown?

This status usually appears when your PDF reader does not recognise the certificate authority. Update Adobe Acrobat or use the EU online verification tool.

Can a signed document be forged?

Not with a PKI signature. Any change to the content after signing invalidates the cryptographic seal — the PDF reader immediately shows it as Modified after signing.

Guides

How to verify an electronic signature on a document

Learn how to verify the validity of an electronic signature — who signed, when, and whether the document was altered after signing.

Medium 5 min 4 steps

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Steps

Step-by-step walkthrough

1

Open the signed PDF

Documents signed via zipzipdoc contain a digital certificate embedded in the PDF. Open the file in Adobe Acrobat or another PDF reader.
2

Check the signatures panel

In Adobe Acrobat click View, then Show/Hide, Navigation Panes and Signatures. You will see a list of all signatures with their status.
3

Check the audit trail

zipzipdoc generates an audit trail — a file with timestamps, IP addresses and OTP verification for each signer. Find it on the zipzipdoc portal next to each document.
4

Use the EU online verification tool

For advanced verification (including LTV signatures) use the DSS portal from the European Commission — the official EU tool for verifying electronic signatures.

FAQ

Frequently asked questions

An audit trail contains: time of sending, time of viewing, time of signing, the signer's IP address, device type and email OTP verification. It serves as electronic evidence in a potential dispute.

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