Microsoft weren't hired by Id to port Doom. They did so exclusively for their own purposes: to show off Windows 95 with DirectX as a performance gaming platform. They licensed the Doom engine, made their own changes, and released Doom 95 usable with a retail copy of the game assets.
Oddly enough, the project of "porting Doom to Windows" was started by Gabe Newell, who worked at Microsoft at the time,
Oddly enough, the project of "porting Doom to Windows" was started by Gabe Newell, who worked at Microsoft at the time,