F.E.A.R. Files

Simple, like it says, just get to this point in the campaign. The difficulty doesn't matter. The achievement just pop after the screen fades out at the end of the mission "Labyrinth"

This is the fifth of six "progress" achievements. You are close to beating the campaign. I think its just 1-2 hours til the end.

Here is a great walkthrough if you get stuck:
http://www.gamefaqs.com/computer/doswin/file/941968/51786