In survival mode, trapdoors can't be crafted.
MCPE-16 Trap doors are not craftable in survival.
MCPE-41 No trapdoors in survival
MCPE-53 no trapdoors
MCPE-58 Trapdoor
MCPE-123 IN Survival, Trapdoors cant be Crafted.
MCPE-231 Trapdoor Missing In Android