How to sign a PDF in Firefox

Add your signature

1. 1

   Open the PDF in Firefox

   Drag the file into a Firefox window, or open it from a link or download. It opens in Firefox's PDF viewer, with the editing tools at the top right.

2. 2

   Choose Add signature

   Click the signature button in the toolbar, then Add new signature. If you don't see it, update Firefox; the signature tool arrived after the other editing tools.

3. 3

   Type, draw or upload it

   Pick Type to write your name in a signature style, Draw to sign with a mouse, a finger or a stylus on a touchscreen, or Image to use a photo of your signature on paper. The trash-can button clears an attempt.

4. 4

   Save it for next time, or don't

   Leave Save signature ticked and it appears in the signature menu next time. Firefox fills in a description for it, which you can edit; it doubles as the signature's name. On a shared computer, untick it.

5. 5

   Place it and download

   Click Add, then drag the signature onto the line and resize it. To keep your changes, download the PDF from the viewer and save it with a new name.

Fill in the rest of the form

• Real form fields: click and type straight into them. Check boxes and drop-downs work the same way.
• Blanks that are just printed lines: choose Text, pick a size and color, then click where the words go.
• Initials or a quick mark: Draw gives you a pen with color, thickness and opacity, handy for initialing each page.
• A stamp or logo: the image button places a picture on the page, with an Alt text button to describe it.

What Mozilla says about this signature

Mozilla's help is unusually direct: a signature added in Firefox's PDF viewer is a simple annotation, with no authentication or verification behind it, and Mozilla says it isn't a legally binding e-signature on its own. In practice that means it works like a signature pasted onto the page. That's often fine for a form you send back yourself to someone who asked for it. It's weak when you might need to prove who signed, and it's not a certificate-based digital signature.

When you need more than a picture

If the signature has to stand up later, or someone else has to sign, use an e-signature service that records the signing. SignMaster runs in Firefox like any website. Upload the PDF, add each signer, place their fields and send. Each signer agrees to sign electronically before they sign, and the finished PDF carries a certificate of completion with their email, IP address and the time of each step, plus a SHA-256 fingerprint that shows if the file changes later. The Free plan sends 3 envelopes a month, and signers never need an account.