very urgnet plz

Dear sirs;
I have small problem in asp.net and now become big .infect i have some html(articals) files witch stores in fodler with name articals . so i want just Paid user can view html files but its not accessable from direct link spouse eye4tech.us/volume/artical/getit.html
i user windows authentication method but using this method i can just restrict aspx file but not html files . so plz whats the way ..is there anyother way to protect html files?
Thanks