Falling
Source Player Core pg. 413
If you fall more than 5 feet, when you land you take bludgeoning damage equal to half the distance you fell. Treat falls longer than 1,500 feet as though they were 1,500 feet (750 damage). If you take any damage from a fall, you land prone. You fall about 500 feet in the first round of falling and about 1,500 feet each round thereafter.
You can Grab an Edge as a reaction to reduce the damage from some falls, or Arrest a Fall if you have a fly Speed. In addition, if you fall into water, snow, or another relatively soft substance, you can treat the fall as though it were 20 feet shorter, or 30 feet shorter if you intentionally dove in. The effective reduction can't be greater than the depth (so when falling into 10-foot-deep water, you treat the fall as 10 feet shorter).
You can Grab an Edge as a reaction to reduce the damage from some falls, or Arrest a Fall if you have a fly Speed. In addition, if you fall into water, snow, or another relatively soft substance, you can treat the fall as though it were 20 feet shorter, or 30 feet shorter if you intentionally dove in. The effective reduction can't be greater than the depth (so when falling into 10-foot-deep water, you treat the fall as 10 feet shorter).
Falling on a Creature
Source Player Core pg. 413
If you land on a creature, that creature must attempt a DC 15 Reflex save. Intentionally aiming yourself to land on a creature after a long fall is almost impossible.
Critical SuccessThe creature takes no damage.
SuccessThe creature takes bludgeoning damage equal to one-quarter the falling damage you took.
FailureThe creature takes bludgeoning damage equal to half the falling damage you took.
Critical FailureThe creature takes the same amount of bludgeoning damage you took from the fall.
Falling Objects
Source Player Core pg. 413
A dropped object takes damage just like a falling creature. If the object lands on a creature, that creature can attempt a Reflex save using the same rules as for a creature falling on a creature. Hazards and spells that involve falling objects, such as a rock slide, have their own rules about how they interact with creatures and the damage they deal.