Anvils let you combine items, including their Enchantments. The primary item is saved and the secondary item is destroyed, with all of its pertinent Enchantments transferred to the primary item. Enchantments that aren’t allowed to affect a specific item aren’t transferred, so they’re simply lost. Thus, you can’t put armor Enchantments on a Bow, even if you combine a Bow with an Enchanted Book that has multiple armor Enchantments. Anvils can also combine two regular items, as long as they’re of the same type. Two Diamond Picks with the same Enchantments can be used on the Anvil together. The second is destroyed to repair the primary.