This has to be done to correctly stop the rust for its also behind the door latch as well. I have this problem on one of mine but its rust bleeding from around the window trim and I'll have to tackle this the same way.

I agree with army. Suggestion, remove the door handle. There is trick I learned. On the back edge of the door, where the catch is there are one or two screws which hold the door handle mechanism in place. Remove these two screws, then either tap the door handle forward or backward and it will release from the door and can be pulled from the car. The whole processes takes about 45 seconds per door.

To tackle the rust it will have to be tackled from both sides. Start be sanding the door to expose about 1 inch of clean metal around the rust area. Apply a rust converter or an eastwood encapsulator to stop the rust and neutralize it. Then apply an etching primer followed by a top-coat repairing the door. This can be followed by a clear coat.
On the reverse side of the door around the door handle, there is probably rust which can be treated with PO15. The trick is to stop the rust from coming back. One way to do this is to stop oxygen from getting to it so as to spread.