Adding pre installed steam game

[76561198062158105]

HI, I would like to ask, I got the left 4 dead 2 for free today, I add it on my library then It ask to be downloaded. The thing is, I already have a steam copy of the game. Can I just use these copy to avoid the download and play the game instantly ?

[TeKraken]

How did you get the game if you already have the game?

And yes you can use the files, steam should say "discovering files" and then update and play.