Ultimate Doom version v1.9 Source port used : ZDoom v2.4.1
The ZDoom game engine is slightly different from the vanilla Doom engine, but the result is reasonably faithful to the original game.
100% secrets achieved in the 3 first episodes. In episode 4, several secrets areas are out of reach in level 3 and 7. This is by design.
There is a cut at 43:05 in episode 2. I removed the goofy part where I run around trying to find the secret door viciously hidden just in front of me. :p Another cut at 41:37 in episode 3. I missed a tricky jump to the secret exit and had to teleport back to do it again.