As the summary states, Iron Trapdoors can be pushed by pistons. Normal Trapdoors have been intended to be pushed, but I'm unsure if the Iron variant is meant to, especially considering it requires redstone to utilize, so moving them via alternative means could circumvent normal protections.

To replicate, place three blocks and place the Iron Trapdoor on the side of the middle block. Place a piston on the side of one of the other two blocks so it faces the Iron Trapdoor. Activate the piston, and it will push the Iron Trapdoor to the next block.

I understand this might be considered Works as Intended, but I'm unsure if it is.