What are the different treatments for decubitus ulcer or pressure sore?

It depends: The best treatment is prevention by relieving pressure which can also help heal early ulcers. If there is significant necrotic tissue or the ulcer is quite large/deep, surgical debridement and closure may be performed. Infections and other problems which delay healing (tobacco, poor nutrition, diabetes)need to be controlled with appropriate treatments as well for best results.

LOTS OF THINGS: Unfortunately like most things with lots of options, none work well for lots of people. Pressure avoidance is the most important thing. After that come good nutrition, lots of protein ( preferably animal based like whey from milk), vitamin c, zinc, and good wound care. Surgically, that includes removal of dead tissue, and then consideration for a surgical closure.