Each release of OS X has brought with it added PDF features in Preview, the Mac’s built in image and PDF app. In Mountain Lion, it is one of the most powerful PDF apps available, rivaling even Adobe Acrobat in many ways. One of more useful new features is the ability to create a digital version of your signature that can be placed into a PDF.
Creating a signature
Start by signing your name on a blank sheet of white paper.
Next, open Preview, and choose PREVIEW, PREFERENCES in the menu bar. Click SIGNATURES in the Preferences window.
Click CREATE SIGNATURE. This will activate your Mac’s iSight camera. Hold the paper with your signature up to the camera so that your signature rests on the blue line in the camera preview on your screen. You will see a preview of how your signature will look to the right. Once it looks the way you want, click ACCEPT.
Click the plus sign in the lower left of the Signatures window to add another signature, or close the Signature window if you are finished.
Adding your signature to a PDF
Open the PDF in Preview, then click in the toolbar (or press Shift-⌘-A) to show the Edit Toolbar.
Now click in the Edit Toolbar, then choose your signature from the drop-down list.
Click and drag on the document where you want your signature placed. Drag out to make your signature larger, or in to make it smaller. When your signature is the right size, release the click, then click in the middle of the signature to drag and fine tune the position of the signature.
Jason Merrill, Mac & iOS Consultant