Hi! You do not need the keys to access any doors in the game, you'll need all of the keys to eventually access an exit door once you get back to the entrance hall at the end of the cyclic path that you have to take in order to access all of the keys. Every room features at least one key (2 at most), so make sure to always examine every room for any hidden keys, going back is quite a risk. Make sure to find a light switch as quickly as possible once entering a room but also deactivate lights you don't need anymore to save energy. Hope this helps!