Do you have to draw an omen/event/item card as soon as you enter the room?
You are able to use items and other actions mid-move, but as soon as you discover a room, your movement immediately ends and you must draw an Event/Item/Omen card before you are able to take any other action.

From the rules (which can be downloaded here) on page 6:


  You can perform actions (such as using an item or attacking) in the middle of your movement. However, whenever a game effect makes you draw a card for any reason, you must stop moving for the rest of your turn.


and


  When your explorer enters a doorway, and there isn’t a room on the other side, look at the top tile on the room stack. .... Then move into that room. You have discovered it.


and then on page 10


  The first time you discover a room with a symbol, you must end your move
  in that room and draw the appropriate card.