E-invoices are new types of invoices, which do not have a traditional form ( paper or electronic file, such as PDF). These invoices have the form of a file in XML format, generated in accordance with the logical structure published by the Ministry of Finance – the so-called XSD Scheme. An e-invoice is issued by sending it to the KSeF, which verifies its formal correctness and, after positive validation, assigns it a unique number.
Source: krgroup.eu
