Drop Forging can be done above the recrystallization temperature when it is called hot forging and below the recrystalization temperature, when it is called cold forging.
Drop Forging can be done using an open die where the flow of the material has to be guided by the operator.
In closed die forging, the ram which hits the billet will have the shape of a die. The material is enclosed between the fixed die and the die on the ram. The material flows to take the shape of the die.