Importing files installed separately into Steam
I already have Path of Exile downloaded and installed from their site. I'd like to add it as a Steam game so I can unlock the various Steam achievements while playing it.
However, Steam insists on downloading the entire several gigs - how do I get it to detect my existing files? I tried download and then cancel it, followed by moving my existing game directory under steamapps/common , but this didn't work.
You can't.
If you want the steam achievements, you'll need to use their version of the game.