Collateral documents for loan are any documents that are required by a lender in order to secure the loan. These documents include promissory notes, deeds of trust, security agreements, and other documents that outline the terms of the loan, such as the interest rate, repayment terms, and any other conditions to which each party must adhere. By providing these documents, both parties have a legal and binding agreement in place to protect their investment should the loan go into default.