I'm no expert, but I personally think it would be quite awkward, and yes, a little rude, to open a folder during the interview- especially to ask questions. If you really want to know the answers- you will remember them, I would think. If you referred to a folder, the interviewers might wonder if you can't remember a couple questions, how are you ever going to remember the 12 cranial nerves or the symptoms of common ocular maladies. If I were you, I think I would just try to remember the questions.