- Launch Preview, and from the Preview menu select "Preferences"
- Click on "Signatures" and then "Create Signature"
- Write your signature on a piece of white paper and hold it up to the camera, try to have it somewhat straight on the blue line and watch the "Signature Preview" pane until you are satisfied with the way it looks
- Click on "Accept" to capture the digital signature
Using the Digital Signature in OS X Preview
- Open the PDF file you want to sign in Preview (you might have to Control-click and choose Open With...to get it to open in Preview and not Adobe Reader)
- Click on the Tools > Annotations > Signatures
- Now click within the document where you want the signature to appear