Show Button when user is Logged In using C# and VB.Net in ASP.Net

Sir i have a application where users should be able to log in and view/download files(.PDF,.JPG). I want to make it so the logged in user can view/download/whatever, but not be able to be accessed by non-users who have the path to the URL.

If you are logged in, you should be able to see and download the file. If you're not logged in, no one can accessed.  

Thanks & Regards,

Shashaank Sharma