Much depends on oil or latex originally as well as what you are applying. It's generally advisable to prime and marks to prevent bleeding. Read instructions on can ,if you still have questions check back.

If they are dirty, I clean with hot water and a cleaning cloth before priming.

If those are hardboard or Masonite doors (moulded hardboard, and they appear to be so) they are already primed. Clean them up, repair the dings, etc., touch up the primer and paint.

thank you!!

Prime the entire door with shellac based primer. if you spot prime, the two different surfaces will absorb paint differently and you will see that spottiness upon completion. The shellac based primer will also seal.