I'm fairly new to Pathfinder and I was wondering if a character could shapechange into something like a door, table, or wall? If not shapechange would polymorph do it? I don't have a particular character in mind, I'm just trying to learn more about the spells.
The shapechange spell is geared around continuous changing into a variety of creatures, and has a list of spells that it encompasses. It doesn't do inanimate objects.
Polymorph any object (the spell which changes objects to creatures, objects to objects and creatures to creatures) is not one of these spells that it can replicate. Turning yourself into a door with this spell probably wouldn't be ideal, because you would actually be a door, with all of a door's usual senses, intelligence and other characteristics for one or more hours (three hours for a wood/metal door the same size as you, one if it's larger or smaller, more hours if the door is made of human flesh...).