So, Burning Disarm says this:
This spell causes a metal object to instantly become red hot. A creature holding the item may attempt a Reflex save to drop it and take no damage
Now, it does specify that the creature needs to be holding the item. It does go on to say that they are forced to take damage if they cannot drop the item:
Circumstances that prevent the creature from dropping the item (such as a locked gauntlet) mean the creature gets no saving throw.
Additionally, it also says that if cast underwater, it boils the surrounding water, insinuating an "AoE" type effect.
So, my question is that for example, if I were to stab an enemy with a dagger, or a sword, could I then cast Burning Disarm on that weapon to cause fire damage? Or can this spell only be cast on a weapon being held?