I'm looking for a chess program which offers to play pawn endgames to improve myself.
For example, can I force Fritz 13 to play pawns endgames? If so, how can I achieve this?
Any chess-playing computer program that allows you to set up positions can be used. And yes, Fritz is especially suited for this.
You have several options:
Set up the position yourself (using board/position set up). Choose any position that you want to get better at. Save that position and play against the computer.
1a. I used to do this for simple pawn endings. I'd play both colors until I figured out some aspects of the pawn ending.
1b. I'd often set up one side with an advantage (say an extra pawn) and see if I could win easily. (Since the computer plays well, this is not easy to do in practice.)
You can start collecting some endgame positions, from a book or from around the web, create a small endgame learning database for yourself, and practice.
In this video (be sure to watch) Nigel Davies recommends Silman's Complete Endgame Course (I find most things by Silman to be very good.)
Finally, if you don't mind spending a little, "Fritz Endgame Trainers" (DVD or software add-ons) that ChessBase sells are quite good. (Just buy one at a time, and be sure to read the reviews to see if it is at the right level for your needs.)
Hope that helps.