A duck can come in the house as long as you let the duck spend most of it's time outside.
Ducks are not good indoor pets as they prefer to be outside.
However it's okay to allow the duck to be in the house once in awhile but do not keep the duck in your house as a house pet like you would a cat, dog, bird etc.
Keeping a duck in the house too much is bad for the duck and is cruel for the duck as ducks are outdoor animals and need to be outside to roam around.
It's best to have at least 1 acre of land or more and a pond for your duck.
I would not want a duck unless I lived in a rural place and could let the duck or ducks walk around the yard.
Ducks are good pets but not good house pets.