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

A digital signature uses public-key cryptography. The signer holds a private key linked to a certificate issued by a certificate authority; signing creates a value that only that key could have produced, embedded in the PDF. Anyone can check it with the public key, and editing the document afterwards makes the check fail.

Because the certificate is issued after the signer's identity is checked, a digital signature says who signed, not just that someone with access to an email signed.

In the US, the ESIGN Act and UETA don't require any particular technology, so a simple electronic signature works for most business agreements. In the EU, eIDAS recognises simple, advanced and qualified electronic signatures; only a qualified signature, made with a certificate from a qualified trust service provider, carries the same effect as a handwritten one in every member state, and some national rules ask for advanced or qualified signatures for certain documents.

India's IT Act 2000 gives legal recognition to electronic signatures made by techniques listed in the Act, which today are digital signature certificates and Aadhaar-based eSign. Agreements made electronically can still be valid contracts under the Act, but check with a lawyer where a statute or a counterparty expects a certificate-based signature.