Iftekhar, As a rule, pressure treated wood will not accept paint well until it has weathered at least a year, and often longer. Even then, special preparation is needed to get a solid bond with paint.
You say this will be an exterior door & mention 8 by 6 by 1; is this 8 feet by 6 feet 1 inch thick? Or do you mean the door will be made from 8 foot lengths of material 1 inch thick by 6 inches wide? And where does this door go; entry door to a home, shed, garage, or will both sides of the door be subject to weather?
Explain a little further & let's see if there wouldn't be a better alternative material for your purpose.