What a digital signature does and doesn't do

A digital signature in Word is a way to mark a document as coming from you and to show that you haven't changed it since you signed it. It's not the same as typing your name or drawing a signature with your mouse. Word uses encryption to create a signature that's mathematically tied to both the document and a certificate that identifies you.

A digital signature proves two things: that the document came from the person whose certificate it is, and that nobody has edited the document after it was signed. If someone changes even one word, the signature breaks and Word shows a warning. This is useful when you're sending contracts, financial documents, or anything else where you need proof of who signed and when.

What a digital signature does not do is hide your document or encrypt it. Anyone can still read the file. If you need to keep the contents secret, you'll need to use a separate encryption tool — a digital signature only proves authenticity and that the document hasn't been tampered with.

Key Takeaways

  • You need a digital certificate before you can sign a document in Word; you can get one from a certificate authority or create a self-signed certificate for personal use.
  • Self-signed certificates are free and work for documents you're sharing with people you trust, but they don't prove your identity to strangers the way a paid certificate does.
  • To sign a document, go to File > Info > Protect Document > Add a Digital Signature, then choose your certificate and click Sign.
  • Once you sign a document, Word locks it against editing; anyone who opens it will see your signature and the date you signed.
  • A digital signature is different from a signature line — a signature line is just a blank space for someone to type or draw their name, while a digital signature uses encryption.

Getting a digital certificate: paid versus self-signed

Before you can sign anything, you need a digital certificate — a file that contains your identity information and a cryptographic key. You have two main routes: buy one from a certificate authority, or create a self-signed certificate on your own computer.

A self-signed certificate costs nothing and takes five minutes to create. You make it yourself using Windows or Mac tools, and it works perfectly well for signing documents you're sharing with colleagues, family, or anyone else you know. The catch is that it doesn't prove who you are to a stranger — anyone could create a certificate claiming to be you. If you're signing a contract with someone you've never met, or a document that will be used in court, a paid certificate is more trustworthy because a third party has verified your identity.

A paid certificate comes from a certificate authority like DigiCert, Sectigo, or GlobalSign. You pay a yearly fee (usually $100 to $300), provide proof of your identity, and they issue you a certificate that proves you are who you say you are. The certificate is tied to your name and sometimes your organization. When someone sees your signature, they know it really came from you because the certificate authority vouched for it.

For most people signing personal or internal documents, a self-signed certificate is the right choice. Use a paid certificate if you're signing legal documents, contracts with outside parties, or anything that might be challenged later.

How to create a self-signed certificate on Windows

On Windows, you can create a self-signed certificate using a built-in tool called SelfCert.exe. Open File Explorer and navigate to C:\Program Files\Microsoft Office\Office16 (the exact path depends on your Office version — it might say Office15 or Office17). Look for a file called SelfCert.exe and double-click it.

A small window will open asking for your name. Type the name you want to appear on the certificate — this is usually your full name, but it can be anything. Click OK. Windows will create the certificate and store it on your computer. You'll see a confirmation message. That's it — you now have a self-signed certificate and you're ready to sign documents.

If you can't find SelfCert.exe, it may not be installed on your version of Office. In that case, you can create a certificate using PowerShell. Open PowerShell as an administrator, paste the command New-SelfSignedCertificate -CertStoreLocation Cert:\CurrentUser\My -Subject "CN=YourName" -KeyUsage DigitalSignature (replacing YourName with your actual name), and press Enter. Windows will create the certificate in the background.

How to create a self-signed certificate on Mac

Mac doesn't have a built-in tool like SelfCert.exe, but you can create a certificate using Keychain Access, which comes with every Mac. Open Keychain Access (search for it in Spotlight), then go to Keychain Access > Certificate Assistant > Create a Certificate.

A dialog box will open. Give your certificate a name, choose "Self Signed Root" from the Certificate Type dropdown, and make sure "Let me override defaults" is checked. Click Create. You'll be asked a few more questions about validity period and other details — the defaults are fine for most people. Click Continue and then Done. Your certificate is now stored in Keychain and ready to use in Word.

Signing a document in Word

Open the Word document you want to sign. Go to File > Info > Protect Document > Add a Digital Signature. A dialog box will open showing your available certificates. Select the certificate you want to use and click Sign.

You'll see a signature details window. This is where you can add a comment if you want — for example, "Approved for release" or "Agreed to terms as of [date]". The comment is optional. When you're ready, click Sign. Word will explore your digital signature to the document and lock it against further editing.

Once a document is signed, anyone who opens it will see a notification at the top saying it has been signed, along with your name and the date. They can click on the signature to see more details, including any comment you added. If someone tries to edit the document, Word will warn them that editing will invalidate the signature and ask if they want to proceed.

The difference between a digital signature and a signature line

Word offers two different features that can confuse people: a signature line and a digital signature. They do different things.

A signature line is just a blank space in the document where someone can type their name or, on a touchscreen, draw their signature with a stylus. It's purely visual — it doesn't prove anything about who signed or whether the document has been changed. Signature lines are useful for documents you're printing out and signing by hand, or for forms where you want a clear place for someone to type their name.

A digital signature uses encryption to prove authenticity and prevent tampering. It's invisible in the document itself — you can only see it by going to File > Info and looking at the signature details. A digital signature is what you use when you need proof that a specific person signed a specific version of a document.

You can use both in the same document: add a signature line as a placeholder, then explore a digital signature to the whole document. The signature line shows where someone should sign, and the digital signature proves that you actually did.

What happens when someone opens a signed document

When someone opens a document you've signed, Word shows a notification bar at the top saying the document has been signed. They can see your name, the date you signed, and any comment you included. If they click on the signature, they can view the certificate details and confirm that the signature is valid.

If the document has been edited since you signed it, Word will show a warning that the signature is no longer valid. This is the whole point — it proves that the document hasn't been tampered with. If someone wants to edit a signed document, they have to remove the signature first, which means the edited version won't have your signature on it anymore.

If the certificate you used is self-signed, Word may show a warning that the certificate is not trusted by the system. This is normal and doesn't mean anything is wrong — it just means Windows or Mac can't verify your identity through a third party. If you're signing documents for people you know, they'll understand that the self-signed certificate is legitimate.

Privacy considerations when signing documents

When you sign a document with a paid certificate, the certificate authority has a record of your identity and the certificate they issued to you. If someone challenges a signature later, the certificate authority can confirm that the certificate belonged to you. This is useful for legal protection but means your signing activity is tracked by a third party.

With a self-signed certificate, there's no third party involved. Only your computer knows about the certificate, and only people you share the document with will see your signature. This is more private, but it also means there's no independent proof that the signature came from you — anyone could create a self-signed certificate with your name on it.

The document itself is not encrypted when you sign it, so anyone who receives it can read the contents. If you're signing a document that contains sensitive information, consider encrypting the file separately or sending it through a find channel.

Frequently Asked Questions

Can I sign a document that other people also need to sign?

Yes. When you sign a document, Word locks it against editing, but you can remove your signature if you need to. The person who receives it can remove your signature, add their own, and send it back. However, once they sign it, your signature will no longer be valid because the document has changed. For documents that need multiple signatures, consider using a service like DocuSign or Adobe Sign that's designed for that workflow.

What if I lose my certificate or switch computers?

If you created a self-signed certificate on one computer, it won't be available on another computer unless you export it and import it. To export, open Keychain Access (Mac) or Certificate Manager (Windows), find your certificate, right-click it, and choose Export. Save the file and import it on your new computer. If you lose the file, you'll need to create a new certificate, but old documents you signed will still show your old signature as valid.

Does a digital signature work in Google Docs or other editors?

No. Digital signatures created in Word are specific to Word and the Office format. Google Docs, LibreOffice, and other editors don't support Word's digital signature feature. If you need to sign a document in a different editor, you'll need to use that editor's signing tool or convert the document to Word format first.

Can I sign a PDF in Word?

Word can open PDFs, but you can't explore a Word digital signature to a PDF file. If you need to sign a PDF, use Adobe Acrobat, Preview (on Mac), or a dedicated PDF signing tool. You can convert a PDF to Word format, sign it in Word, and save it as a PDF, but the signature will be tied to the Word version, not the final PDF.

Is a digital signature the same as a password-protected document?

No. A password-protected document prevents people from opening or editing it without the password. A digitally signed document can be opened and read by anyone, but the signature proves it came from you and hasn't been changed. You can use both together — password-protect a document and then sign it — but they serve different purposes.