The SAF-T is a specification for a computer-readable file that transfers accounting data from the original accounting system into a predefined format derived from XML and makes it available for tax authorities for external auditing. The SAF-T (PT) file is intended to facilitate the collection of relevant tax data in electronic form by tax inspectors to aid taxpayers’ tax returns and/or analyze accounting records. In this regard, the SAF-T (PT) document requires an XML structure. There is no specific format for invoice status. Interested parties can agree to use existing standards (EDIFACT, X12, XML). SAF-T must be manufactured on a computer system approved by the Portuguese Tax and Customs Administration (Autoridade Tributária e Aduaneira – AT). It must be declared through public network services. The invoice to be sent to the customer must contain the SAF-T file and a unique code that was received from AT with the response. This code contains the signature of the previous invoice so that invoices are guaranteed one after the other. It is possible to summarize how SAF-T (PT) works: sales invoices (documentos comerciais a clientes), transport documents (documentos de transport), and customer payments are recorded directly in the accounting system. A standard SAF-T (PT) file in XML format is created from the data processed in the accounting system. This file is the source for the tax return. All of this information is sent to the last AT. Sales are transmitted to AT via the finance portal (Portal das Finanças). Transport documents (transport documents: Guia de Remessa, Guia de Transporte, invoice) are sent to AT after a standard SAF-T (PT) file has been created in XML format.