Poker hands have EXACTLY FIVE CARDS, no more, no less. If there's a royal on board, the best 5-card hand anyone can make is the royal, so the pot is split. (Same with any A-high straight on board, or quads with an A).
If the board is one pair, it depends: if it's A-A-K-Q-J, and no player has a second pair or any card higher than a 10, the the pot is split. If it's A-A-9-7-5, and One player has K-3, he defeats a player with Q-10, because A-A-K-9-7 is higher than A-A-Q-10-9. But he would not defeat a player with K-2, because neither the 3 nor deuce play in the first five cards.