Can you cut MDF with a circular saw?

You can - but try a small cut first as some blades with BIG teeth will not give you the smooth cut you want. Yes - the Mask. VERY important. Protective Glasses too. Save you a few hours in the Accident Room getting your eye popped out with 2 warm spoons!

Certainly! But do use a good sharp blade with smaller teeth (smaller teeth = smoother cut), take your time, wear safety glasses and a dust mask as this stuff is the worst when it comes to being dirty/dusty when you cut it!

If a really smooth cut is important to your project, you can take a razor knife and a long straight edge and score the cut before you make it. This breaks/cuts the surface layer so it doesn't splinter. Not easy but it helps! And you can fill any chips with either wood putty or Bondo for a really smooth finish. But the Bondo stinks to high heavens! It works, but man, it stinks!

yes you can ..but wear a mask ..the dust is considered dangerous

Yes but, very dirty.