Minecraft wiki entry for Pillager, associated text: Iron equipment drops have a 50% chance to be enchanted at level 5-19. Said equipment may also have enchantment combinations that cannot be normally obtained, such as Blast Protection and Fire Protection on the same pair of boots.
Iron equipment drops are always of 30 to 90% durability.
These drops are affected by the Looting enchantment.
Enchanted books have level 30 enchantments, which can also be treasure enchantments.