Which document serves as an assurance that the check will be paid due to sufficient funds?

The document that serves as assurance that the check will be paid due to sufficient funds is a certified check. A certified check is one that has been verified and guaranteed by a bank. When a check is certified, the bank ensures that the account holder has the necessary funds in their account at the time it is certified, and these funds are set aside specifically for that check. This added security makes certified checks a reliable form of payment, as the recipient can be confident that the check will clear.

In comparison, other options do not provide the same level of assurance. Bank acceptances involve temporary transfers of funds between banks but are not direct indicators of sufficient funds in that manner. A promissory note represents a promise to pay a specified sum of money at a future date but does not guarantee that funds are readily available in an account at the time of issuance. A demand draft is similar to a check but typically involves the bank creating the draft rather than the individual, and while it does involve a payment guarantee from the bank, it does not specifically originate from an account holder's available balance like a certified check does.

Thus, the certified check stands out as the most definitive assurance of payment due to available funds.