checking file is mounted at the end of a url

Hi, I'm building a site where among other things, the user (librarian) can see if a file has been mounted on a local webserver for students to download. I could provide a link so they can see if the file (pdf) can be downloaded, but I'd rather just say 'yes' or 'no'. This requires the page doing some sort of url test and reporting yes/no depending on the code being sent back. I found something called linkchecker at Hotscripts.com but when the file doesn't exist, it tries to download itself instead. The user will be accessing my server but will be checking something at their location. I'm sure this must be possible - can anyone point me in the right direction? Cheers George