I had a contract that I needed to sign and fax to someone, but I don't have a fax machine at home. Instead, I printed and signed the signature page, scanned it, merged it back into the contract in the right place, and send it via email as a PDF file. Here's how I did it.
Multivalent is an excellent Java toolkit for manipulating PDFs. I downloaded Multivalent20060102.jar from http://multivalent.sourceforge.net/download.html, which has a hyperlink to the SourceForge download page, saving the jar file to c:/opt/multivalent. The two Multivalent tools I used were Split and Merge.
Using OpenOffice, I saved the document as a PDF. I split the file into two parts, omitting page 5, the signature page:
$ java -version
java version "1.5.0_06"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-b05)
Java HotSpot(TM) Client VM (build 1.5.0_06-b05, mixed mode)
$ java -cp c:/opt/multivalent/Multivalent20060102.jar tool.pdf.Split -page 1-4 contract.pdf
$ mv contract-x.pdf pp1-4.pdf
$ java -cp c:/opt/multivalent/Multivalent20060102.jar tool.pdf.Split -page 6 contract.pdf
$ mv contract-x.pdf p6.pdf
I printed, signed, and scanned the signature page, and saved as p5.pdf. Then I merged the contract back together:
$ java -cp c:/opt/multivalent/Multivalent20060102.jar tool.pdf.Merge pp1-4.pdf p5.pdf p6.pdf
$ mv pp1-4-m.pdf contract-signed.pdf
It was all set, and I emailed it away.
Update of 2008-11-12: PDF Split and Merge is a GUI-based tool that does the same thing.