Normally, an unarmed creature attempting the "Disarm" combat maneuver suffers a -4 penalty on their attack (CMB) roll.
Pilfering Hand allows a caster to attempt to disarm from a distance using an invisible, telekinetic force. I assume the -4 penalty for being unarmed shouldn't apply to a caster making a disarm check from a distance. (According to the spell, attempting to disarm with Pilfering Hand does not provoke an AoO.)
If this -4 "unarmed" penalty does apply to a disarm check using Pilfering Hand, wouldn't a caster just have to make sure they had a dagger in hand while casting the spell, thereby becoming "armed"? It strikes me whether or not a caster 30' from the target has a weapon in hand or not shouldn't affect the disarm roll.
Or would you always apply the -4 penalty to a Pilfering Hand disarm check, since the telekinetic hand of force is always "unarmed"? (This would imply its harder to knock an opponent's weapon out using an invisible, closely-controlled and manipulable hand of force rather than a weapon.)
In our house rules, we've ruled the unarmed penalty does not apply to the Pilfering Hand disarm check. However, I'm thinking of adding this spell to a PFS character, so I thought I'd check to see if our interpretations were outside of the mainstream before I spring this on a GM in organized play.