villagers don't have a durability trade notion except when giving you something with less durability. you can trade anything to them no matter the durability as long as they accept it as an item.
as far as items giving you enchants when held.. they don't exist without a large amount of command blocks.. potion effects can only be consumed or splashed in vanilla.
the only things you can do with "held" items are attribute modifiers such as max health, max attack, knock back resistance, movement speed and attack speed- all of which are against the vanilla rules for player based items.
me putting bow enchants on a sword is within the creative realm of items books and anvils.