8.5 ～ないでください

Question 1

How can you request someone to refrain from doing something?

Answer 1

negative verbal short form + でください

Question 2

May I enter this room?

Answer 2

このへやにはいってもいいですか？

Question 3

Please don’t enter this room.

Answer 3

はいらないでください。
(入ってはいけません　implies youre an authority and is too strict)