If you’re looking for the ‘quick n’ dirty’ solution GIMP is the answer. You’ll need some good texture workflow tutorials to get started and GIMP has a bit of a learning curve, but not too hard if you just need some convincing scratches. Also scratch brushes abound on the web if you need more options.
However! if edges is all you need to affect, the geometry node pointiness value is your new friend.
Hope that helps.
Oh! last note, Another option,
you can texture straight inside blender with, again, some good tutorials: Blender GURU’s Anvil Tutorial | beginner texturing
Hope this isn’t too much scattered information and is actually helpful.
