It is a quest reward for completing the quest Unfathomable Depths.
- With the 25% bonus, a fully-upgraded set of Dwarven Armor can give a slightly higher armor rating than fully-upgraded Dragonplate Armor, depending on the skill.
Ancient Knowledge gives 25% armor bonus to all armor types except Dwarven armor. This can happen even after the official patch 18.104.22.168.8 that supposedly has the fix for the bug.
- The Unofficial Skyrim Patch seems to fix this.
- Even though the effect's description says it only improves how fast Smithing can level up, it may improve how far armor and weapons can be upgraded instead.