first issue, is the wall load bearing? If so, you will need the kings and headers and all the cripples installed for support of ceiling.
If not a load bearing, you might be able to do without the header depending on the width of the door. The header could be as much as a 2x4 on the cripples. The furdown or drop ceiling will present allot of issues to overcome. You will still have to open up the furdown to make the modifications.
This is very difficult to give advice on with this limited information. How low is the drop ceiling, what is the height of the intended door, is it a load or non load wall. Is there electricity running in the wall, if so you have to go up and over the door and into the furdown anyway.