Error message saying couldnt find original disc.

I just downloaded Stronghold 2 off of BitTorrent and used Daemon Tools to install the game on my computer. When i click on the game to play it, it says couldn't find original disc. I was wondering how to get around this. I looked at other forums and someone said something about a .nof file but i could not find it or know what to do. So, if there is anyone that can help me I would appreciae it. Thanks