Sounds harmless ..right? But if you place your aquarium near a window you can have several problems. Firstly the temperature of your water could be effected,when your freshwater aquarium has long periods of sun on it the temperature will rise and thus affect the fishes. Consider not puttng it there or add curtains to keep the heat off. If you live in a cold country then its the opposite drafts or chilly air can lower the aquarium temperature,so therefore its easier to avoid windows full stop.
Another factor that you must consider is algae growth. placing a tank near natural sunlight will increase the growth of algae by many fold. Once algae begins to overrun your aquarium, it can be really difficult to get of.

So you can see windows are a no go for aquariums.
Doors

Exterior doors can be very drafty, and placing your aquarium near them will lower the temperature of water. Place your tank well away from any outside doors to avoid drafts.

Interior doors have other issues, not from the cold but from the door hitting the aquarium, most door knobs are at the right level to hit the tank. WIth a hard bang from a door knob and yur fish could be swimming on the floor. So before fixing the location test out the door to ensure it will not hit the tank.

For more information on Location of Freshwater Aquarium click here.