The pilot of the float equipped fishing lodge airplane instructed his passenger, a guide employed by the lodge, to exit the airplane's cabin and stand on a float in preparation for docking at a remote site. The pilot reminded the guide, a new lodge employee unfamiliar with aircraft, to stay behind the door until he shut the engine off, and the propeller had stopped. The guide did not stay behind the door, but walked forward on the float prior to engine/propeller stoppage. The guide was fatally injured when he was struck by the propeller.