If your talking about the trim on the outside of the doors, it is called a bump strip. It is put there to protect the door from "door dings" caused by doors of other cars. It can be installed by the individual owner, or if enough customers are concerned, the dealers may put them on all their stock. It is usually held on by an adhesive, so a little bit of heat to soften the glue and pulling it off will remove it, followed by a light cleaning to remove any residue.
