A portamedic is a separately contracted company, that sends a person to your home or office or allows you to go to them and they perform a physical of sorts determined by the contract they have with the OP.
Most do not draw blood or gather a urine speciman.
Usually they take your vital statistics...BP, Pulse, respirations, weight...and may ask about drug allergies...

Pretty much what happens before see you a doctor at the office, when the nurse comes in first and takes your temperature etc...

Generally a fast and painless experience.