The official Guild Wars 2 Wiki has an article on damage (calculation).
Edit: I'll try to sum it up for you, as damage coming through depends on several factors.
The damage you deal can be raised if you score a critical hit: 1% crit dmg per trait point.
Condition damage can also add to the total. +10 cond dmg per trait point.
Effective damage you do is also dependent on the level difference. Then there are the mechanics of sidekicking and scaling, the Protection boon, positioning, projectile distance, ... that are all part of the complete formula.
The wiki article has since been updated, and now contains an easy to understand formula to calculate direct damage.
Damage done = (weapon damage) * Power * (skill-specific coefficient) / (target's Armor)
Armor only mitigates direct damage, so condition damage and falling damage is not mitigated by armor.