How to tell whether a PDF is really digitally signed
Actualizado el 18 July 2026
You open a PDF, you see a signature with somebody's name and a date, and you assume it's signed. In plenty of cases, it isn't. What you're looking at is just a drawing pasted onto the page. This confusion causes real problems when that document reaches a bank, a court or any body that actually validates signatures.
A digital signature is not a visible seal
A digital signature has two parts, and they're worth keeping apart:
- The visible part: the squiggle, the name and the date you can see on the page. It's only a drawing.
- The invisible part: a cryptographic certificate embedded in the file that guarantees who signed and that the document hasn't been altered since. This is the one that counts.
The problem: the drawing can exist without the invisible part. A document can look signed without being signed.
How the signature is lost without you noticing
The cryptographic signature covers an exact sequence of bytes in the file. If the PDF is modified in any way — merged with another, compressed, converted — those bytes change and the signature stops being valid. Some tools also delete the drawing when they do it, so you find out. Others keep the drawing but destroy the real signature, and there you don't find out: you're left with a document that looks like what it isn't.
How to check it yourself
- Open it in a serious reader (Adobe Acrobat Reader, for instance). If it has a real signature, a signature panel appears at the top saying whether they're valid. If nothing appears, there's no signature.
- Click on the signature. If it's real, a window opens with the certificate, the issuer and the date. If nothing happens, it's an image.
- Use a signature inspector. Our free Signature inspector reads the internal structure of the PDF and tells you straight away whether there's a real digital signature, who signed it and when — without uploading the file to any server.
Why it matters
If you send a document you believe is signed and it isn't, whoever receives it may reject it or — worse — accept it without knowing it has no validity. In official paperwork, contracts and declarations, the difference between "looks signed" and "is signed" is the difference between valid and void.