Which document serves as primary evidence of debt?

The promissory note serves as the primary evidence of debt because it is a written promise from the borrower to pay a specified amount of money to the lender at a defined time. This document outlines the terms of the loan, including the interest rate, repayment schedule, and the parties involved. It creates a legal obligation for the borrower, making it the fundamental instrument that represents the borrower's commitment to repay the loan.

In contrast, a letter of credit is a financial document issued by a bank or financial institution guaranteeing the payment to a seller on behalf of the buyer, but it does not serve as a record of a debt owed by the borrower. A deed of trust, typically used in real estate transactions, functions as a security instrument that creates a lien against the property to secure the loan but does not serve as a direct record of the debt itself. A bill of sale, on the other hand, is a document used to transfer ownership of personal property and does not pertain to debts in the context of loans or borrowing.