16. Digital Signatures

From the early days, Adobe has wanted contracts and other agreements in PDF format to be legally binding documents. To do this, there needed to be some way of electronically signing a PDF document so that it was unimpeachably certain that a particular person had agreed to its contents.

This problem has been thoroughly solved; electronically signed PDF files are accepted as legally binding documents by many federal agencies and state governments, including the Internal Revenue Service and the State of California. In this chapter, we shall see how to sign a PDF document and how to confirm that the signature on a signed document is valid.