There’s no good reason to print a document just to sign it. Once you create a digital image of your signature, you can simply “paste” it onto a PDF.
Signing PDFs using Adobe Reader
Adobe, creators of the PDF standard, produced this comprehensive video that shows how to create a form people can sign as well as several ways to sign such a form (starting at the 1:50 mark).
Note: Adobe Reader XI includes “touch-friendly” mobile apps that let you draw on PDFs with your fingers.
Signing PDFs using Preview (Mac only)
The Mac OS contains a versatile application called Preview. One thing it does is easily handle PDFs, letting users read, annotate, add pages to and – you guessed it – sign PDFs.
This short video shows how you can use Preview to sign PDFs.