How to Add a Digital Signature to a PDF

'Digital signature' actually covers two pretty different things, and knowing which one you need matters more than most people realize.

Electronic signature vs. a real digital signature

An electronic signature is typically a drawn, typed, or uploaded image of your signature dropped onto the page. Fast, and fine for most everyday paperwork — but it doesn't cryptographically prove who signed or that the file hasn't been touched since. A true digital signature uses a certificate-based key that does both, and that's what's required for legal, government, or high-stakes business documents.

Adding a simple one

Upload the PDF, draw your signature with a mouse or trackpad, type your name in a script font, or upload a photo of your handwritten signature. Place it, save it. Fine for informal agreements and internal approvals.

Adding a certificate-based one

This needs an actual digital certificate — from a certificate authority or generated in signing software — and produces something that verifies cryptographically and flags a warning in PDF readers if the document changes after signing. That's the one you want for contracts and legal filings.

When several people need to sign

Decide upfront whether signers go in order or all at once — some documents genuinely need sequential signing, others don't. And track which version each signer is working from, so signatures don't end up on an outdated copy.