Is it correct to say Dr Smith MD.?

"Doctor" is an honorific. If you're addressing him personally, "Dr. Smith" is better; if you're writing it somewhere, it's fine (and may in some cases be preferred) to add the specific degree(s) and societies: "Dr. Fred Smith, MD, FACS." Particularly in lists this is useful, as it may help distinguish Fred Smith the surgeon from Fred Smith the dentist.