If you don’t, there are lots of very cheap ways to grab them:
In order to do this you need to legally own the full games already on PC. Now if you want to use QuestZDOOM to play the original DOOM, DOOM II, Heretic, or Hexen, you can do that as well - including with some of the great mods available. The user interface isn’t great for VR, it’s basically a giant window that looks like an old-school PC game launcher, but it works well enough. It’s all pretty straight forward with lots of options. From there you’ll select which core game files to launch, such as FreeDoom, followed by any other assets or mods you want to enable. Once installed, start the ‘launcher’ application from your list of Unknown Sources in the Library tab inside your headset. You can either follow the links above or locate the launcher and the QuestZDOOM engine in SideQuest’s Games and Apps tab or search bar.