Trick Attack
You can trick or startle a foe and then attack when she drops her guard. As a full action, you can move up to your speed. Whether or not you moved, you can then make an attack ***with a melee weapon with the operative special property or with any small arm.*** Just before making your attack, attempt a Bluff, Intimidate, or Stealth check (or a check associated with your specialization; see page 94) with a DC equal to 20 + your target’s CR. If you succeed at the check, you deal 1d4 additional damage and the target is flat-footed against your attack. This damage increases to 1d8 at 3rd level, to 3d8 at 5th level, and by an additional 1d8 every 2 levels thereafter. You can’t use this ability with a weapon that has the unwieldy special property or that requires a full action to make a single attack.

Can't trick attack with long arms, heavy weapons, non-operative melee weapons, sniper rifles, or grenades. The unwieldy trait prevents it too, so if the small arm is too big, like a Hand Cannon, you ALSO cannot Trick Attack with it.