Hello, to answer your question the answer is no, portable air conditioners do not need a window. A portable air conditioner is meant to be portable, well a some window ACs have to be mounted through the wall, or placed in a window but window ACs are usually very heavy while most portable air conditioners have wheels, making them easy to move from one room to another room. I prefer a portable air conditioner to a window AC because a they crank out just as much cool air as a window one, and they cool off a whole room fast. If you have limited space in your place than I recommend that you get a portable one instead of one meant for the window.
Another thing I would like to point out is that a lot of people get portable air coolers and portable air conditioners confused with one another. Coolers are just as portable as portable ACs but they use water and evaporation to cool while air conditioners that are portable use a compressor and coolant to cool which makes them much more effective at cooling rooms while also keeping the humidity low. If you are going to get an AC than definitely go and buy a portable air conditioner because they are much easier to use and move around than window ACs. How this helps.