"-4 penalty on attack rolls, saves, ability checks, and skill checks."
Does it apply to damage as well or just to-hit rolls?
"-4 penalty on attack rolls, saves, ability checks, and skill checks."
Does it apply to damage as well or just to-hit rolls?
As a Damage roll is not one of the listed types of rolls, it does not apply to those.
That particular section of Bestow Curse does not affect damage dealt, only the character's chance to hit. [As well as their Saving Throws, Skill Checks and Ability Checks].
However, if you chose to decrease an ability score -6 (naming strength) as with one of Bestow Curse's other options then the target's melee damage and melee chance to hit would both be reduced while the curse was active.