We double a natural NT bid where it’s 2 against 1, or 2 against 2 and the contract is 2+NT. If 1 against 1, double is takeout of a minor, so 1D-(1N)-P-(P)-X is takeout of clubs, and 1H-(3N)-P-(P)-X is takeout of either minor. If 2 against 2, a double of 1NT is responsive or support. So, (1D)-1H-(1N)-X is responsive, typically 5-2 in the majors, and 1C-(1D)-1S-(1N)-X is support.
In other words, doubles of specifically 1NT are for penalties when we have both bid but only one opponent has bid. Doubles of 2NT are for penalties if we have both bid.