I have a basic webpage that has a couple links that users can go to download certain document viewers. If the client has not downloaded the viewer, it prompts them to download it and if it already have been downloaded then it goes directly to the login page for the software that uses that type of viewer.

The problem is... that users don't always know if they have downloaded it before and click on the link to download it. If it already has been downloaded it takes them directly to that login screen. They don't want them to go directly to the logon screen at that point. They want them to do a check first to see if the file(s) exist and if they do take them to a different page where it tells them they already have the viewer installed. How would I write the code that would check the PC that the user is on to see if the file exists and if it does redirect them to another page and is that possible to be checking files on the user's own pc - is there some security implications?

Any help or advise would be appreciated.