Digital signature
Also known as: electronic signature, e-signature, sign a PDF
A digital signature on a PDF marks who signed a document and confirms it has not been altered since. It ranges from a simple drawn or typed signature image to a cryptographic signature backed by a certificate that can be mathematically verified.
- Marks who signed and whether the file changed afterward
- Ranges from a signature image to a certificate-backed signature
- Cryptographic signatures detect any later tampering
Simple vs cryptographic signatures
At the basic level, signing a PDF means placing an image of your signature — drawn, typed, or uploaded — onto the page. This is fine for everyday agreements and is what most people mean by an e-signature.
A true cryptographic digital signature goes further: it uses a certificate to bind the signature to the exact contents of the file, so any later change breaks the signature and reveals tampering. This is what gives legally binding e-sign services their integrity guarantee.
Signing on your device
Signatures add negligible size to a PDF — a small image or a block of certificate data. The document itself stays the main storage cost.
To place a signature on a document without extra software, /tools/sign-pdf lets you draw or upload one and position it on the page, then export the signed PDF.