I used a heat gun to take off paint how do i get the brown stuff still on the doors?

Answer 1

That brown stuff may be stain that was on the doors before they were painted. Sanding the doors is the only way to remove the stain.

Answer 2

If the heat gun made the brown stuff sticky without removing it, it is probably varnish in which case in can be removed with a chemical stripper such as Nitromors and steel wool (No 4 Grade).
If it was not affected by the heat gun then it is woodstain and this can only be removed by sanding or bleaching but it could be a long job.

Answer 3

SANDPAPER and sweat