restrict users to other users files in the same folder

I have a 1000 users. Each user has a pdf with ther username in the file name in a folder. All pdf's are in the same folder. When a user logs in there is a link to their pdf. All one has to do is change the url to a different username to see another's pdf. I need to stop this. All the user's pdf files have to be in the same folder for production reasons.
I thought of copying the user's files to a temp folder, then delete it when the user logs out ot the session ends. The copy code works, but I can't get the delete code to work. I put the delet code in the global file.
    Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
        Dim thisVersion As String = AppSettings.Item("majorVersion")
        Dim facilityID As String
        facilityID = User.Identity.Name
        Session("User") ...