A document issued by the seller`s own courier and signed by the customer to acknowledge receipt of the goods is?

The document you are referring to is called a Delivery Note. A Delivery Note is a document that is issued by the seller's own courier (or delivery person) and is signed by the customer. The purpose of this document is to acknowledge that the customer has received the goods that were sent by the seller. This document serves as proof of delivery and shows that the goods were received by the customer in good condition. It is an important document for both the seller and the customer, as it helps to avoid disputes about whether or not the goods were received.