Primer is not metal so can't rust and it still acts as a barrier from the outside. If its just a pea size, then its worth just buying the correct touch up paint and filling in the gap. As its primer you can just put the touch up paint straight on top.

Hi if it is that small consult with a body shop depending on the age of the car it might not be worth doing anything about it.

Sand it down and repaint it. Where it is no ones going to notice unless the door is open, a quick Saturday morning fix.

lol, only you noticed it. get urself an angle grinder and cut it out. or take it to A&E ,this requires major surgery

Hello

I bought the car 2 months ago and today inspecting by opening the passenger door(the inner part where the door seal meets with the gap when you close the door). I noticed there was a pea size or a bit bigger shape which the paint layer has come off and judging from it, it is at the Primer layer.

Could the primer layer of paint rust/corrosion and do you think I should get the area fixed by taking it to a body shop?