You can use a file on a remote Unix machine as if it were on your local machine. This is useful for reading PDF documents you left on your desktop at school and don't want to scp to home. To do it use the command:
ssh -X firstname.lastname@example.org
After you have authenticated and are sitting at the command prompt on the remote machine, run the desired application on the remote machine's command line like this:
The document will open using the local version of xpdf, (it must exist on the local machine to work, and remote machine aswell) but will display the remote document.