can't unzip

[cluckenbell]

I have recently bought a digital copy of amnesia the dark descent, and I am thoroughly dissatisfied due to the fact that each time I try to unzip the file an error comes up stating that the file is invalid, I would like to have some form of consolation from this game that I have purchased. I would also like to state that I have downloaded the game multiple times and the same error message keeps coming up.