Waht causes pulmonary edema?

Many things: Anything that allows fluid to leak from the blood or lymphatics into the lung tissue and air spaces. Infection, heart failure, sever protein malnutrition, trauma, kidney failure, etc can all do it. Overwhelming the hydrostic equilibrium or decreasing the oncotic pressure all allow fluid to move into the lung.

Many causes, heart: Pulmonary edema can be caused by many things - but by far, however, the most common cause is heart failure. In this scenario - the left side of the heart cannot keep up with demand and essentially fluid "backs up" into the lungs (this is an oversimplification and doesn't discuss lymphatic flow, the starling curve, oncotic pressure etc. Etc.) but we only have 400 characters here.