Refer to figures.
Profile Drag or Rotor Profile Drag is the drag created when the rotor is moved through the air, even when no lift is being generated and it is made up of the blades':

• Form (pressure) Drag
• Skin friction Drag

In general, form drag is caused by the form or shape of the object travelling through the air. It can be reduced by streamlining the object, i.e. designed so that its curves present the least possible obstacle to flowing air. Streamlining can produce a radical reduction in drag, with the radical reduction in pressure force on the object, if we first add front and back curves to make it a sphere and then elongate the rear curve to streamline it further. Thus, the shape of the front and back of a blade is a factor that affects the form drag.

Skin Friction Drag is the drag resulting from the friction between the surface of an object and the molecules flowing close to it. It takes place very close to the surface (typically just a few millimetres) in an area called the Boundary Layer. Right at the surface of the object, air molecules are slowed and brought to a complete standstill relative to the aircraft's surface. Skin friction drag does not affect form drag, but is just added to it and all together make up the Profile Drag.