The most common misunderstanding in this whole area sounds like this: “but we have been sending invoices electronically for years”. An electronic invoice in the legal sense is something different from an invoice sent electronically.
A PDF is not an e-invoice
An electronic invoice is a structured XML document following the European standard EN 16931 in one of the permitted syntaxes — UBL 2.1 or CII. An accounting system can read and process it on its own, without anyone retyping the data.
In the Peppol network the Peppol BIS Billing 3.0 profile is used in practice, which is built on UBL; the law itself does not narrow it to a single syntax.
A PDF or a scanned document does not meet that condition — those are images. A human can read them; a machine cannot.
Which documents travel over the network
The eFaktúra system carries documents that qualify as invoices under § 72 of the VAT Act:
- invoices,
- self-billing invoices — the buyer issues the invoice on the supplier’s behalf,
- credit notes.
Which do not
A proforma invoice or a request for payment is not an invoice under the VAT Act — issuing it creates no tax liability and it is not sent over the network.
Note the distinction: if you receive a payment before the supply of goods or services, an invoice for that payment must be issued under § 72(1). Such a document does qualify as a tax document and must go over the network.
Summary invoices
A summary electronic invoice covering several separate supplies is possible, but only for a period of at most one calendar month (§ 85o(7)).
Corrections
An invoice sent into the network cannot be withdrawn. The usual correction path is the same as on paper:
- issue a credit note against the original invoice,
- send a new, correct invoice.
The alternative is a corrective invoice, which must satisfy all Peppol BIS
Billing 3.0 requirements and carry an unambiguous reference to the original
invoice in the BT-25 field.
Archiving
The taxable person must retain the electronic invoice for ten years from the end of the calendar year it relates to (§ 85o(15)). It must be kept in XML format — in the form in which it was issued and delivered, not as a printed or converted document.
Source
Financial Directorate of the Slovak Republic, 9/DPH/2025/IM — Frequently asked questions on eInvoicing; Act No. 222/2004 Coll. on VAT as amended by Act No. 385/2025 Coll.