Digital Signature (PDF)
A cryptographic signature embedded in a PDF that proves who signed it and that the file has not been modified since.
A digital signature on a PDF is a cryptographic artifact that proves two things: (1) the identity of the signer, and (2) that the document has not been altered since it was signed. It's substantially stronger than a drawn signature or a typed name.
Digital signature vs electronic signature
These two terms are often confused but mean different things:
- Electronic signature (e-signature). A visual representation of a signature — drawn with a mouse, typed with a fancy font, or pasted as an image. Legally valid for most everyday contracts in most jurisdictions (ESIGN Act in the US, eIDAS in the EU).
- Digital signature. A cryptographic signature backed by a certificate from a trusted authority. Provides stronger proof of identity and tamper-evidence. Required for certain regulated workflows (government filings, healthcare, some financial documents).
How digital signatures work
A certificate authority (like DocuSign, Adobe Sign, or a national ID card) issues the signer a private key. When the signer applies the signature, their private key cryptographically signs a hash of the document. Anyone with the signer's public certificate can verify the signature — and any later change to the document invalidates it.
Tools
- Sign PDF adds an electronic signature to a PDF — draw, type, or upload an image of your signature.
- Flatten PDF locks the signature into the page content so it cannot be moved or edited later.
For certificate-based digital signatures that carry legal weight in regulated contexts, you'll need a dedicated service like Adobe Sign or DocuSign — browser-based tools cannot issue the required certificates.