What a digital signature does in Word

A digital signature in Word is a way to sign a document electronically using your computer. It proves the document came from you and hasn't been changed since you signed it. When you add one, Word attaches an invisible encrypted marker to the file that contains your name, the date and time you signed, and a unique code only you can create.

This is different from typing your name or drawing a signature with your mouse. A digital signature is cryptographically secure — meaning someone cannot forge it or alter the document without breaking the signature. Word shows readers whether the signature is valid and whether the document has been modified after signing.

You can sign a Word document yourself, or you can set it up so others must sign it before they can edit it. Most people use digital signatures for contracts, agreements, official forms, and any document where proof of who signed and when matters.

Key Takeaways

  • You need a digital certificate (a file that proves your identity) before you can add a digital signature to a Word document.
  • You can get a free self-signed certificate from your computer, or purchase one from a certificate authority for stronger security.
  • Once you have a certificate, you add your signature through Word's Sign button in the File menu, which takes about two minutes.
  • After you sign a document, Word locks it against editing — readers can view it but cannot change it without removing your signature.
  • If you want others to sign the document, you set up signature lines before sharing it, and they sign using the same process.

Get or create a digital certificate

Before you can sign anything, you need a digital certificate — a file that identifies you to Word. You have two options: create a free self-signed certificate on your computer, or get one from a certificate authority (a company that verifies your identity and issues official certificates).

For most personal and small business use, a self-signed certificate works fine. Word will warn readers that it cannot verify who you are, but the signature will still prove the document hasn't been tampered with. If you need others to trust that you really are who you claim to be — for legal contracts or official documents — buy a certificate from a certificate authority like DigiCert, Sectigo, or GlobalSign. These cost between $100 and $400 per year.

To create a free self-signed certificate on Windows, open the Start menu and search for "IIS". Click Internet Information Services (IIS) Manager. In the left panel, click your computer name. In the center panel, double-click Server Certificates. On the right side, click Create Self-Signed Certificate. Give it a name (like "My Signature"), choose a location to store it, and click OK. On a Mac, you'll need to use Keychain Access — search for it in Spotlight, then go to Keychain Access menu and select Certificate Assistant, then Request a Certificate From a Certificate Authority. For most Mac users, purchasing a certificate is simpler than creating one yourself.

Insert a signature line in your document

Before you sign, you should add a signature line — a visual placeholder that shows where the signature goes. This is especially important if other people will sign the document, because it tells them exactly where to click.

Open your Word document and click where you want the signature line to appear. Go to the Insert tab at the top. Click Signature Line (you may need to click the arrow next to it if it's grouped with other options). A dialog box opens. Type the name of the person who will sign in the "Suggested Signer" field. Add their title in the "Suggested Signer Title" field if you want. You can also add instructions in the "Instructions to the Signer" field — for example, "Please sign this document to confirm you have read and agree to the terms." Click OK.

Word inserts a line with an X box and the signer's name. This is just a placeholder — it doesn't actually sign anything yet. If you're signing your own document, you can skip this step and sign directly. If others will sign, send them the document with these lines already in place.

Sign the document yourself

Once you have a certificate and your document is ready, signing takes just a few clicks. Open the document you want to sign. Go to File in the top left. Click Info. On the right side, click Protect Document, then click Add a Digital Signature.

A dialog box appears asking you to choose which certificate to use. If you created a self-signed certificate, it will appear in the list. Click it to select it. If you purchased a certificate from a certificate authority, it will also be listed here. Click the certificate you want to use, then click OK.

A second dialog box opens showing your certificate details. You can type a reason for signing in the "Purpose for Signing This Document" field — for example, "Approved for release" or "Agreed to terms." This reason is recorded with the signature. Click Sign. Word signs the document and locks it. You'll see a notification that the document has been signed.

What happens after you sign

Once you sign a document, Word marks it as final and prevents editing. Readers can open it and view it, but they cannot change the text, add comments, or modify anything without first removing your signature. If someone tries to edit it, Word will ask them to remove the signature first — and if they do, the signature becomes invalid and readers will see a warning.

You can see signature details by going to File, then Info, then View Signatures. A panel opens on the right showing who signed, when they signed, and whether the signature is valid. If the document has been changed since signing, Word displays a red X next to the signature and says "This document has been modified."

If you need to make changes to a signed document, you have to remove the signature first. Go to File, Info, View Signatures, right-click the signature, and click Remove Signature. The document unlocks and you can edit it. Once you're done, you can sign it again.

Set up a document for others to sign

If you're creating a document that multiple people need to sign — a contract, agreement, or approval form — insert signature lines for each person before you send it out. Add the lines in the order people should sign them, and include clear instructions about what each person is approving.

When you send the document, tell the signers to open it, find their signature line, and double-click the X box. They'll be prompted to select their certificate and add their signature. Each person's signature is added to the document in order. After everyone signs, the document is locked and cannot be edited without removing all signatures.

You can also set up a document to require signatures before anyone can edit it. Go to File, Info, Protect Document, and click Restrict Editing. Choose "Tracked Changes" or "Comments Only" to allow those actions, or choose "No Changes (Read Only)" to lock the document completely until it's signed. This forces readers to sign before they can make any edits.

Troubleshooting common signature problems

If you see a message that says "No certificates found," you don't have a digital certificate installed yet. Go back to the "Get or create a digital certificate" section above and create a self-signed certificate or install one you purchased.

If the signature shows as invalid or you see a red X, the document has been modified since it was signed. This is Word's way of warning you that something changed. Ask whoever modified it why, and consider having them re-sign if the changes were intentional.

If you're on a Mac and the signature line doesn't appear in the Insert menu, you may be using Word in a limited mode. Make sure you're using the full version of Word for Mac, not Word Online. Word Online does not support digital signatures.

If you want to sign a document but don't see the Protect Document option in the File menu, your document may be in a format that doesn't support signatures — like .docx files created in very old versions of Word. Save it as a modern .docx file and try again.

Frequently Asked Questions

Can I sign a document without creating a certificate first?

No. Word requires a digital certificate before you can add a signature. You can create a free self-signed certificate on your computer in about five minutes, or purchase one from a certificate authority. Without one, the Sign option will not work.

What's the difference between a self-signed certificate and one from a certificate authority?

A self-signed certificate is free and proves the document hasn't been changed, but Word cannot verify that you are who you claim to be. A certificate from a certificate authority costs money but includes verification of your identity, so readers can trust the signature is really from you. For contracts and official documents, a purchased certificate is stronger.

Can I remove a signature after I've signed a document?

Yes. Go to File, Info, View Signatures, right-click the signature, and click Remove Signature. The document unlocks and you can edit it. Once you remove a signature, it's gone — you'll have to sign again if you want the signature back.

What if someone else signs my document and I want to add my signature too?

You can add your signature after someone else has signed. Open the document, go to File, Info, and click Add a Digital Signature. Word will add your signature alongside theirs. Both signatures remain valid as long as no one edits the document after the last signature.

Does Word Online support digital signatures?

No. Digital signatures only work in the desktop version of Word (Word for Windows or Word for Mac). If you're using Word Online in a web browser, you cannot add or view digital signatures. You'll need to download and open the document in the full version of Word.