I'm guessing you mean the door jamb material which is painted the same as the door brickmold trim. Let me guess...The jamb is wet at the bottom areas and decayed?
If it is really big ...like a baseball size..you could cut out the damaged part with a chisel and square it off, then install a custom fit piece of pine and use some wood bondo. Wood bondo filler is a 2 part mix. Just like the car stuff. Then primer and paint. It may not look the best but the other option is removing the door and changing the whole jamb...or door.
Like Daryl say's ,pictures are fantastic.
Let us know.