Ok, so First off, you must set Doom to run in Vulkan API mode, instead of OpenGL. This is done in Advanced settings of Doom game.
Also, as mentioned, your game must be cracked, so it runs without steam. because if Steam preloader is present, then RenderDoc can't hook in.
1. Put in path to Doom Vulkan Executable.
2. Make sure Ref All Resources is Checked.
3 Press Capture to start the game.
Once you get to a scene in the game with content you want to get textures for, Press F12. That will capture the Frame.
(note that if you don't have an overlay as shown in the pic below, then RenderDoc isn't hooked in properly. This would usually mean your game isn't cracked.
Once you hit F12, the game will seem to freeze, but be patient, it's saving the Frame to disk. each frame is around 1 Gig of data or more, takes some time. You can take multiple frames, just be sure you have enough disk space.
after you exit the game, RenderDoc will still be running, with a screen showing all the frame you took (they call them logs). choose which log to view.
1. Switch to Texture Viewer.
2. Select Inputs tab.
3. Find a Colour Pass entry with large vkCmdDrawIndexed() calls (first parameter is data block size) This is where major geometry is being rendered. Usually the virtualtexture will be present there.
1. Select the VmtrphysicalPagesmap on that entry, and then you can access it's slices and save them as described above.