Digital Signature PDF

How do I digitally sign a PDF with a certificate?

Choose the PDF, then choose your certificate file (.p12 or .pfx) and type its password. Pick whether a signature box shows on the page, and where. Press Sign PDF, then Download. The tool checks the signed file before you save it, and readers show who signed and when.

1. Press Choose a PDF.
2. Press Choose certificate, pick your .p12 or .pfx file, and type its password.
3. Choose the page and position for the signature box, or turn the box off.
4. Press Sign PDF, then Download.

What is the difference between a digital signature and an electronic signature?

An electronic signature is any sign of agreement, such as a typed name or a drawn signature placed on the page; Sign PDF does that. A digital signature is a cryptographic seal made with a certificate. It names the signer and breaks if anyone changes the file afterward, which a picture of a signature cannot show.

Our guide Electronic vs Digital Signature tests both on the same contract and sums up what US and EU law say.

Where do I get a certificate to sign with?

Three common routes: your employer or government may issue one, often on a smart card or as a .pfx file; a certificate authority sells signing certificates that PDF readers trust out of the box; or you can make a free self-signed one, which readers show as unverified until the person checking chooses to trust it.

How do I check if a PDF signature is valid?

Choose the signed PDF above. The tool lists every signature and says whether the bytes it covers are unchanged and whether the signature matches the certificate inside it. It also shows the signer, the issuer, the certificate's dates and the signing time. Trust in the issuer and revocation are not checked here.

For each signature, the tool hashes the exact bytes the signature covers (everything except the signature itself) and compares the result with the hash the signer sealed. It then checks the seal against the public key in the signer's certificate, using your browser's built-in cryptography. A single changed byte fails the first check.

How fast is it, and how much bigger does the PDF get?

Signing took 0.13 to 0.17 seconds for each of our test files on a laptop, because it needs one hash of the file and one key operation. The file grew by 16 to 21 KB each time: room for the signature and certificates, plus the signature box. Larger files take longer only to hash.

Measured on 12 October 2026 in Chrome 152 on an i5-8350U laptop, with a visible signature box on the last page. Time is the middle of three runs and includes reading the certificate. Every signed file passed the tool's own check.