Do I take one card in a room or take all?

Question

When I investigate a room, do I take one card per action turn at a time or do I take them all on that action turn?

Answer 1

You resolved them one at the time from the top. Unless you fail a puzzle or is lacking an item this usually means that you take all the cards as one action.
If you find a puzzle in the top of the pile then you can resolve it in that turn and still take all the other cards on the pile, all in one action.