Where can I find the serial number after installation?

[BlueBaron]

I'm trying to play a .bat custom game, but when I go to open it, it asks me for the serial number. I bought the retail version of this game in a store, but I left the box in my dorm at college (I'm home for the weekend). My friend and I wanted to play this custom game over the weekend but I dont have the box with the serial number. Is there somewhere in my root folder where I can find it? Thanks!

[Tanshaydar]

Copy the installkey file in your Documents/Amnesia/Main folder to Documents/Amnesia/<total conversion name> folder.