Thin gold films grown on mica were investigated with the scanning force microscope. By rising the set-point force of the microscope working in the constant-force mode holes and grooves were created in the films. Two basic mechanisms of thin film modification were observed : cutting of gold grains, and displacement of grains on the mica substrate as a whole. Small grains were moved on the mica substrate with forces of only a few nN. Bigger grains could be crushed or cut by the tip when forces in the range of mu N were applied. Using this technique lines could be written in the films.