It was at one point.
If you bought the "Demo" verision of Quake 1, which came on CD-ROM, it had Wolfenstein 3D, all of the Doom and Doom II games, and the full version of Quake 1 encrypted on the disc. The way it was supposed to work, it would provide a code, you'd call id Software, give them a credit card, they'd give you the counter-code, and it would decrypt the installer for whatever game you bought.
But someone released a program that would genereate countercodes for the disc, so they pulled it off the shelves.
I have that disc somewhere...