As usual I feel I have the gist of it rather than the exact details, so a shaker of sodium chloride kept on hand is advised.
Proper demons come in two varieties, unique and non-unique. Unique are the ones what lead goblin civilizations. Non-unique are the regular mob of trash you'd find when you gate crash the "circus". Regarding armor, they're huge. Regarding skills, an equally skilled dwarf usually will lose to an equally skilled demon due to various special abilities the demons have. Incidentally, while a demon's fighting skills are always good, dwarven soldiers who have been training for many years should greatly outmatch them skill-wise.
Meanwhile, necromancers. These guys can create various creatures: unintelligent or intelligent undead, and experiments.
In spite of the name I don't think what you have on hand is a proper demon. It's a necromancer experiment. They are highly variable in form, size, and composition. You said it is "small", which suggests dwarf/elf sized armor. I could be wrong though and small in this case means smaller than a dwarf. Anyway, as far as fighting goes, tied in with their own special abilities an experiment would be a durable opponent, but they are not on par with real demons.
Also, you should be able to look at it and see what it's wearing. Fair warning, it might just be bare assed naked with no armor at all. Squint a little to blur things up a bit before you look.