how to download file from File server

Question

We are trying to set up a file server to keep all types of files.
My problem is best way to achieve downloading/opening of file from file server
in already existed asp.net web application without making any code change in application itself
if that is possible.
Currently all files reside in application folder itself
and application navigates to that filepath and opens the file.

I thought creating custom HttpHandler and placing it dll in bin so that I do not need to make change
in code. But i think it will not going to invoke the handler when user click to the link that navigate to
the specified filepath. Please correct me if i am missing something and guide with this problem.

Thank you.