Converting Disc games to steam games?

[Linkos]

Is it possible to convert a game you already had, and make it as you've bought it from steam? (to access achievements, invites, etc.) For EXAMPLE: I bought Unreal Tournament 3 years ago, and found out they have it on steam too. And now i want to be able to access those steam features with unreal Tournament, but how?

[Sepioth]

Not unless the CDKey that came with the game works on Steam can you add it to Steam.

Try the CDKey and see it it accepts.

Here is a list of acceptable games but it is not 100% complete.
https://support.steampowered.com/kb_article.php?ref=7480-wusf-3601

It appears that that game is on the list so if you still have the CDKey enter it into the Steam client. Option is on lower left of client window

Add Game> Activate Game