The difference between UBL, XML and PDF: why a PDF is not an e-invoice
"I already send my invoices digitally by e-mail. Why do I need to change anything?" It is a question many Belgian self-employed professionals ask themselves. The answer lies in the difference between a PDF and a genuine e-invoice.
A PDF is not an e-invoice
A PDF invoice sent by e-mail is digital, but it is not an electronic invoice in the legal sense. A PDF is essentially an image of an invoice — a computer cannot automatically read or process it. Someone has to manually re-type the data into an accounting or ERP system.
A true e-invoice is a structured digital file that can be processed automatically by software. No manual work, no re-typing, no errors.
From 1 January 2026, the PDF invoice is no longer valid for B2B transactions in Belgium. Full stop.
What is XML?
XML stands for eXtensible Markup Language. It is a file format that stores data in a structured way that computers can read. An XML file looks rather cryptic to a human — it is essentially code — but software can process it perfectly.
An XML invoice contains all invoicing data — amounts, VAT, supplier, client, payment terms — in a standardised format that can be automatically imported by any accounting application.
What is UBL?
UBL stands for Universal Business Language. It is a specific standard for XML documents used for business documents such as invoices, quotations and orders.
Peppol BIS is the version of UBL that is mandatory in Belgium (and across Europe) for e-invoicing. It is the language that all Peppol systems speak — whether you use Belgian, Dutch or Italian software.
How does Peppol fit in?
Peppol is the network. UBL/XML is the format. You send a UBL invoice via the Peppol network — think of it as e-mail (the network) sending a specific file type (the format).
As a business owner, you do not need to understand this distinction to work with it. Your invoicing software ensures the invoice is automatically created in the correct UBL format and sent via Peppol. You simply see a normal invoice on your screen — the software does the technical work in the background.
Can an invoice be both a PDF and an XML?
Yes, and that is actually the most user-friendly solution. A Peppol BIS invoice typically contains a structured XML file for automatic processing, plus a readable PDF or HTML version for anyone who wants to view it themselves.
This means your client receives an invoice that their accounting software processes automatically, as well as a version they can read and archive themselves.
In summary
- PDF: readable for humans, not automatically processable by software — no longer valid for Belgian B2B invoices
- XML: a structured file format that software can process automatically
- UBL: the specific XML standard for European e-invoices
- Peppol: the network over which UBL invoices are sent
You do not need to arrange any of this yourself. Cleero automatically creates the correct UBL invoices and sends them via Peppol. Try it free.