Final answer:
Willem's business likely sent a Credit Note to Erari Traders to acknowledge the return of damaged goods and to indicate the buyer's account was credited.
Step-by-step explanation:
When Willem's business returned some damaged goods to Erari Traders, the document they would have sent is a Credit Note. This document is issued by a seller to a buyer. It serves as a way to acknowledge the return of goods that were damaged or not as per the order. The Credit Note also indicates that the account of the buyer has been credited with the value of the returned goods, thus reducing the amount the buyer owes to the seller.