This is perhaps an odd or silly question, and it needs a bit of elaboration.
I have two copies of a game, one from Steam, and one from the developer's website. This is because I purchased the game before it became part of a Humble Bundle. In the case of Arkham Asylum, there is a mac version of the game, but Steam does not carry it. They DO carry Arkham City's mac version, though. Darned if I know why.
I've looked in the package content of Steam games before, and they come with extra files, namely on how to handle Steam integration. I'm going to try to replicate these files into my mac copy of the game, with all the symlinks. I want to see if this will allow Steam to track my data in the game, mostly, such as time played and achievements earned. If this is not possible, I won't be heartbroken. I know this is a stretch at best. I come here because I've scoured the internet in search of an answer to this, and this is the last place I can think of.
Has this been done before? If so, to what degree of success? Am I crazy to think that this replication might work?
Thanks.
Best Answer
Unfortunately not - the best you're going to get is the Steam overlay and screenshot support if you add the game to Steam as a non-Steam game.
Integration for Steamworks and integration into the Steam client for activities such as playtime tracking, cloud integration, update management, achievement tracking, Steam Workshop, etc, simply isn't possible.
Here is some associated reading for previously asked (similar) questions on this subject:
How do I associate a Steam game with a separate, non-Steam install?
Is there any point in adding a non-Steam game to Steam?
What advantages do I gain from playing a game through Steam?
How do I see screenshots taken through Steam of a non-Steam game?