If you are going to be painting them, then you will need to seal edges. The simplest way is to take drywall compound, slightly runny, and smear on edges with finger. When dry, sand off excess. then prime. Did this last week on a panel to cover a hole ( not made by me) on a job. Really did a good job of sealing edges so they looked like face of MDF when painted. WOW! Remember that a sheet of 3/4" MDF weighs 94 pounds, so when at borg get one of the flat top carts to carry and be sure to get a "loader" to help you. Definition: loader- the guy who watches you struggle with sheets of MDF, then asks cute blonde if she needs help with a piece of shoe moulding.