A portable air conditioner will not work properly without being vented to the outside.
So you don't really need a window for the portable air conditioner to work but you do need to have a way for the hose of the portable air conditioner to vent to the outside otherwise you'll just be dumping the hot air back inside the house.
A portable air conditioner needs to be vented through a window or out some other opening to the outside otherwise the portable air conditioner will not work.