There must be a unique link between the original document and the data processing document. It is therefore extremely important to organize how original documents are filed. SAP recommends the following procedure:

Always store your original documents under the processing document number.

For customer documents, you either use the document number created by a pre-invoicing system, or have the system assign numbers using the internal number assignment function. To transfer billing documents from the R/3 billing system, you need to create document type RV, which has internal number assignment, or RX, which has external number assignment, in Financial Accounting. The billing system uses these document types to transfer documents. When internal number assignment is used, the system assigns a new number to each document in the Financial Accounting component. In external number assignment, the system transfers the billing document number to the FI document as long as this number has not already been assigned.