The example.enc is an example text file that is encrypted for the following people via PGP keys:
  Kevin A. McGrail
  David Jones

It is a way of testing that you have encryption/decryption working well.

To decrypt (if you are listed above):
gpg --output example.enc.txt example.enc

To encrypt after modifications:
gpg --sign --encrypt -r kmcgrail@apache.org -r davej@apache.org < example.enc.txt > example.enc

Need to import someone's public key? I use gpg --import with their public key block from people.apache.org.