A: No. Wizards of the Coast does not release full sourcebooks for free. The only free material is the occasional preview (usually one adventure or a few magic items) released via news articles.

While there is no legal way to download the entire Keys From The Golden Vault

"Keys From The Golden Vault" is significant for several reasons:

The rumors in the seedier taverns of Neverwinter whispered of a collection of blueprints—the ultimate guide to the multiverse's most secure locations. They called it Keys From the Golden Vault