Guides

Plain guides to how e-signatures work, for people who build things. Our view runs through all of them: the record of how a signature happened matters more than the mark on the page.

What these are

Each guide answers one question. They are general information, not legal advice. Laws change and differ by place, so ask a lawyer about your own documents.

All guides

• How to sign a PDF

  To sign a PDF yourself, use the free tool already on your device: Preview on a Mac, Acrobat Reader on Windows or Android, Markup on an iPhone. When someone else has to sign, or you need proof of who signed and when, send it through an e-signature service instead.

• How to sign a PDF on a Mac

  Open the PDF in Preview, show the Markup toolbar, click Sign, and pick or create your signature. It's built into every Mac, it's free, and the file never leaves your computer.

• How to sign a PDF on Windows

  Windows has no built-in signature tool like a Mac's Preview, so use the free Adobe Acrobat Reader: open the PDF, choose Fill & Sign, add your signature, and save. Microsoft Edge can also draw on a PDF in a pinch.

• How to sign a PDF on an iPhone

  Open the PDF in the Files app, tap the Markup button, tap the plus button, choose Add Signature, and sign with your finger. It's built into iOS and iPadOS and costs nothing.

• How to sign a PDF on Android

  Android phones don't share one built-in signing tool, so the dependable free route is the Adobe Acrobat Reader app: open the PDF, choose Fill & Sign, draw your signature, and save.

• How to sign a PDF on a Chromebook

  Use the Gallery app that comes with ChromeOS: open the PDF, select the signature button, draw your name, choose Place signature, and save. It's free and needs no install. Chrome's browser tab can't do this, so open the file from Files.

• How to sign a Word document

  Word gives you two built-in options. A signature line marks where someone should sign. A scanned picture of your handwriting puts your actual signature on the page. Neither records who signed or when.

• Electronic vs digital signature

  An electronic signature is a legal idea: a person showing they agree, by drawing, typing or clicking. A digital signature is a technical one: maths over a file that shows it hasn't changed since it was signed. A good e-signature process uses both.

• Is an electronic signature legal?

  Yes, in the US and for most business documents. Under federal law, a signature or contract can't be denied legal effect just because it is electronic. But that rule only gets you in the door. Whether a given signature holds up depends on what you can prove.

• The ESIGN Act and UETA, for builders

  ESIGN is the federal law and UETA is the state law, and together they ask very little at the moment of signing. If you build signing into software, you owe three things: agreement to go electronic, a consumer disclosure when a law requires a writing, and records people can keep.

• What is PAdES?

  PAdES is a standard for putting digital signatures inside a PDF, so anyone can check that the file hasn't changed. It proves the file is intact since a moment in time. It doesn't prove who a person is, and people mix those up all the time.

• How to add e-signature to an app

  Call an API to create the document, let the signer use a hosted page, listen for a webhook, and store the sealed file. You can do that in an afternoon. Don't build the signing page yourself, because the evidence is the hard part.

• Can an AI agent sign a contract?

  It shouldn't, and in docuinked it can't. US law lets automated systems take part in a contract if their actions are attributable to the person bound. That is exactly why you want a hard line: prepare by machine, approve and sign by person.

• E-signature audit trails, explained

  An audit trail is the record of how a signature got onto a document: who was sent what, when, from where, and what they did. In a dispute it does more of the work than the signature, because a signature can only be denied, and a record can be explained.