Do you have to do damage for Armor piercing to take effect? example, if you have 3 targets and 2 damage, can you do damage to all three?

First yes, then no.

If you have 3 targets and two damage, you could put one damage on two of the 3 targets, and deal one irreduceable damage to both targets. The third could not receive any damage. The reason for this is because Armor piercing only keeps your damage from reducing below one, it does not grant you that one damage.

ok, thanks.