How to sign a PDF — and what makes a signature legally binding

“Signing a PDF” covers three quite different things in 2025, and they aren’t interchangeable. Picking the wrong one for the wrong document is the most common e-signature mistake we see.

The three kinds of e-signature

1. Simple electronic signature (SES). A typed name, a drawn signature, or a scanned image dropped onto the page. Fine for everyday correspondence, internal approvals, and most low-value contracts.
2. Advanced electronic signature (AES). Uses cryptographic identity that ties the signature to the signer. Common in enterprise software with audit trails.
3. Qualified electronic signature (QES). An AES issued by a regulated trust service provider. Legally equivalent to a handwritten signature under EU/UK eIDAS.

What works for what

For NDAs, freelance contracts, supplier paperwork and similar everyday documents, a simple electronic signature is generally enough in the UK, EU and US. For property transactions, certain employment paperwork in some jurisdictions, and anything that has to stand up in court, a QES is the safer choice.

How to add a simple signature in your browser

The PDFSamurai sign tool (coming soon) lets you draw with a touchscreen or trackpad, type a stylised version of your name, or upload an existing signature image, then place it anywhere on any page. The result is a normal PDF file you can download immediately. Nothing is sent anywhere; the signed file exists only on your device.

Common mistakes

• Using a photo of a signature taken on a sloped surface — alignment looks off in print.
• Forgetting to date the signature alongside it (where required).
• Sending a signed PDF without flattening it, so the signature image can still be moved.