A per diem form is a document used for reimbursing employees for meals and lodging expenses incurred while traveling for business purposes. The main purpose of the form is to provide a record of the expenses incurred by the employee while traveling for work.
A credit note is a document used in business transactions in which an issuer, such as a vendor or seller, authorizes a credit against their accounts receivable balance to a buyer, typically for items that have been returned or overcharged. It can also be used to adjust an invoice or correct an error.
A Debit Note is issued by a customer to a supplier as a means of formally requesting a credit note. a supplier might also issue a debit note instead of an invoice in order to adjust upwards the amount of an invoice already issued (as if the invoice is recorded in wrong value)
A Proforma invoice is an invoice provided by a supplier in advance of providing the goods or service. A quotation in the form of an invoice prepared by the seller that details items which would appear on a commercial invoice if an order results.