Electronic vs digital signature: what a signed PDF actually proves

An electronic signature is any electronic mark that shows a person agreed to a document; a digital signature is a specific cryptographic technique that also proves which certificate signed it and that the document has not changed since.

Every digital signature is a kind of electronic signature. Most electronic signatures are not digital signatures. A typed name at the end of an email, a click on "I accept", and a picture of your handwritten signature placed on a PDF are all electronic signatures — and none of them is a digital signature.

1. 1

   The document is fingerprinted

   The signing software calculates a hash of the file — a short value that changes completely if a single byte of the document changes.

2. 2

   The fingerprint is encrypted with your private key

   Only the holder of that key can produce this result. The key belongs to a certificate issued to a named person or organisation.

3. 3

   The reader checks it

   When the PDF is opened, the reader recalculates the hash, checks it against the signature using the public key in the certificate, and checks that the certificate is one it trusts. If anything was edited after signing, validation fails.

For most everyday business paperwork, the question is not "can this be forged" but "did this person agree". A drawn or uploaded signature answers that well enough, because the evidence is the whole exchange: the email it came back in, the account it came from, and what both sides did next.

• The person or authority asking says "digitally signed", "certificate-based", "qualified" or names a specific signing service.
• The document will be checked by software rather than read by a person — some government portals and tender systems reject files without a valid signature.
• You need to prove later that the document was not altered after signing, against someone who might dispute it.

In those cases a picture of a signature will not do, however neat it is. You need a signing certificate — from an e-signature service, your employer, or the certification provider the requesting authority names — and software that signs with it.

Many legal systems accept electronic signatures for ordinary contracts and then set stricter rules for particular documents. In the United States, the ESIGN Act (2000) and the state UETA laws provide that a signature cannot be denied legal effect solely because it is electronic. In the European Union, the eIDAS Regulation (EU) No 910/2014 defines three levels — electronic, advanced and qualified — and gives a qualified electronic signature the same legal effect as a handwritten one. Saudi Arabia's Electronic Transactions Law (2007) gives electronic records and signatures legal effect, subject to the conditions it sets.

Sign & Stamp PDF places an electronic signature: you draw it or upload a picture of it, place it where it belongs, add a stamp, initials or the date if needed, and download the file. The signature is drawn into the page itself, so it appears in every reader and survives printing. The whole job happens in your browser — the document is never uploaded.

It does not create certificate-based digital signatures. That needs a private key held on your behalf, and holding keys would undo the reason every PDF tool here runs on your own device. If you have been asked for a certified signature, use a service that issues one.