Invoice is the general term for a legal document that a seller issues to a buyer, which shows a list of products or services that have been provided to the buyer and also shows how much the buyer has to pay according to the terms of payment. An invoice will also be a delivery order (D/O) as a record of delivery. In practice, the buyer will keep an original invoice as a record of buying, and the seller will keep a copy of invoice as a record of selling. However, not every invoice is acknowledged by the revenue department(RD) because some invoices always miss out details required by the RD such as the seller's tax registration number (or tax ID number) ans the buter's full name and address.