An electronic invoice is not simply an invoice sent by email in PDF format. It is a document that is issued, transmitted, and received in a specific digital format – designed to be automatically read and processed by accounting systems without the need for manual data entry.
In the European Union, the standard for such documents is the so-called UBL (Universal Business Language) – a structured XML format that defines how invoice data should be recorded and organized. Thanks to UBL, the system knows exactly where to find the invoice number, sale date, or VAT rate and can process them automatically.
Importantly, an e-invoice must comply with the European standard EN 16931, which ensures uniformity and interoperability of documents across different EU countries. This means that regular PDF, Word, or paper invoices will no longer be sufficient – they do not meet the requirements for automated data processing.