Electronic invoices


Electronic billing, or electronic invoicing refers to the digital transmission of an invoice, typically a file, from a sender computer to a recipient computer. This can e.g. be a XML file by email, a PDF download from a web portal, but it can also be a computer fax between two computers. If a dedicated protocol for the transmission of electronic invoices is used, it is still an electronic invoice, even a structured one, but more narrowly this is already called Electronic data interchange. In that particular case (of EDI) you might not even see a file.

Electronic invoices does not automatically mean you also have to pay electronically, however, the recipient can still pay how (s)he likes, e.g. in cash. It is under your responsibility to pay the invoice, but at least structured and hybrid electronic invoices will state very clearly what has to be paid when to whom under which reference, so your banking software can present you a “balance this invoice” button.

Structured vs unstructured

Unstructured invoices are human readable, for example the image file of a scanned paper invoice. PDF files may contain a text layer, which can be used for OCR data if it is a scan. But even if this text may allow for copy&paste the precise meaning of the amounts are not defined in a machine readable way, both PDF files with and without text layers are still unstructured: a software would have to guess the meaning of a particular amount or a user would have to at least manually approve according assignments.

The meaning in a structured electronic invoice is usually expressed in a XML syntax: XML invoices are usually structured invoices. It defines data and meaning but it does not define a layout.

Structured electronic invoices are already obligatory for B2G invoices in some countries and will become also mandatory in germany.

Structured invoices can by hybrid or native.

Hybrid vs native

A invoice XML file, carrying the meaning of all items and attributes is typically a native structured electronic invoice: it does not carry layout information how to optically display it. So the layout of a print is not defined, the recipient would have to define that e.g. the total amount is to be displayed at the bottom right of the document. There are many native formats and versions, UNCEFACT CII and UBL are just two examples and there is a very nice comparison between UBL and UN/CEFACT available.

These formats require specialized reader software (standalone or integrated in your ERP) capable of understanding it and presenting it to the user: You can automatically check the calculation but for the correctness, also native e-invoices usually have to be manually approved.

Hybrid e-invoices define both meaning and layout. Factur-X/ZUGFeRD define the invoice layout in a conventional PDF file, so you can use any PDF reader to access the invoice. The meaning (which amount is which tax amount and so forth), is additionally defined in a XML file which is embedded into the PDF file.

Since PDF readers are widely available, many recipients can use=pay the invoice manually “as usual”. The XML information will be used automatically if (s)he has a suitable specialized reader or ZUGFeRD capability integrated into her ERP system.

The FeRD published Guidelines for companies regarding electronic invoices. And E.ON Energie Deutschland GmbH produced a very basic (german) explanatory film on hybrid B2C e-invoices:

Pro hybrid invoices

  • The reader software (PDF reader) is widely available.
  • The sender does not have to know if the recipient is private, govermental or business customer and if a agreement has already been accepted.
  • The invoice layout can be very close, if not identical, to printed invoices.
  • The recipient and the sender can easily print hard copies.
  • No fixed cutover date is necessary: due to the integrated fallback hybrid invoices can be introduced gradually.
  • Invoice content and layout can be archived together.
  • Service providers can digitalize a paper invoice and send the recognized invoice together with it’s raw image data.
  • Additional files like time sheets or measurements can be included in the same invoice PDF file.
  • The invoice can be digitally signed, which is still a requirement in some european countries like Hungary.
  • Hybrid invoices (no prior agreement, wider availability of reader software) are more suitable for use in the B2C sector. (like e.g. used by EON or Conrad ) context.

Contra hybrid invoices

  • Even if they are easily printable it is usually not sufficient to archive only a printed copy.
  • Not only valid XML but also a valid carrier format like PDF-A is required.
  • Only a few hybrid invoices will not save sufficient time to replace legacy workflows.
  • People might continue to use the human readable part only.
  • The decision if the machine or human readable part is used has to be documented in the process
    documentation in some countries like Germany.
  • There is usually little indication that a machine readable part exists.
  • If the fallback is intact the sender might not even be notified if the machine reable
    part is incomplete or corrupted.
  • Hybrid invoices have a bigger filesize and require a layout, e.g. a letterhead.
  • It is technically hard to automatically guarantee that the invoice layout (the human readable PDF “image”) matches the XML content. An attacker could send optically correct invoice PDFs with embedded counterfeit XML content. The attack will succeed if only the optical representation is checked, but the XML part is processed.

Use cases

Have magic scans (hybrid only)
Some service providers scan paper invoices for their customers and delivers them as PDF. Since anyway already a optical character recognition (ORC) was run on the scans, they now also offer the service of semi-automatic invoice recognition and add manually corrected (and therefore guaranteed) ZUGFeRD metadata to their scans so that they can be automatically processed.
Facilitate Procure-To-Pay (hybrid and native)
When companies use ERP systems where

  • orders are entered into the system and
  • the storage facility registers every delivered item upon arrival in the system and
  • the invoice arrives as ZUGFeRD and refers to the order

The invoice can be automatically checked vis á vis the order and can be automatically payed and booked as envisaged when creating the order.

Have your suppliers in line (hybrid and native)
Some bigger companies have managed to persuade a significant amount of their suppliers to send ZUGFeRD invoices. This way they save money because no paper or unstructured PDF invoices need to be processed.
Pay invoice files (hybrid and native)
ZUGFeRD means no more need to copy&paste IBAN, amount or purpose field for a bank transfer, it’s sufficient to select the ZUGFeRD-PDF file to be paid. This can e.g. be done with the open source onlinebanking software Hibiscus or a commercial product called CIB SEPArator which converts ZUGFeRD files to SEPA XML.

European Situation


Some countries introduced mandatory electronic invoices in the B2G sector, Denmark was the first in 2005, followed by Sweden 2008, Spain and Finland 2010 and Austria and Italy 2014.

Probably also because already in 2009, Denmark could credibly explain that the e-invoice saves them 100 million Eur/year. The predicted savings vary in a great bandwith, in 2010 the European Commission referred to  a report
which indicates 226 billion Euro savings potential within six years (“assuming the best case scenario” and “a linear evolution”). In 2014, the EU finally decided in their 2014/55 EU Guideline to make the support of electronic invoices mandatory for all member states.

The EU legislation ignores unstructured electronic invoices and defines electronic invoices as “an invoice that has been issued, transmitted and received in a structured electronic format”. This definition is not yet consistent through the laws of all countries, which might have led to confusion, e.g. Germany’s e-Rechnungsgesetz / e-Rechnungsverordnung follows this definition, whilst the german law on VAT (Umsatzsteuergesetz) speaks of electronic invoices without further qualification and covers both structured and unstructured invoices. This unclear definition, often omitting the qualification “structured”, has caused some confusion, e.g. a german article stating that 68% of the participants in a survey (the article probably refers to this) do not know what electronic invoices are.

The European standardization authority CEN has followed it’s duty and published EN16931 to augment 2014/55/EU.

You can buy EN16931 from your national standard body but after a lengthy discussion at very high levels (further details (german)) it has been agreed that the first part of the standard, EN16931-1, which details on the calculation rules, numbers of decimals etc., are published free of charge (german version).

In the meantime, CEFDIGITAL has published a very helpful lists of all codes which can be used in EN16931 files, e.g. for currencies, countries, means of identification and units.

Switzerland followed with electronic invoices in 2016. Germany national authorities will start accepting electronic invoices as of November 2018 and make it compulsory as of November 2020 on a federal level.


Electronic invoicing is voluntarily in the B2B sector.

In Austria, e-invoices are more or less treated like digital versions of the printed invoices, which makes it very easy to handle with. Austrian companies might even be allowed to destroy paper receipts after scans.

In Hungary, apparently e-invoices have to be digitally signed.

Regarding Switzerland, in 2018 Simone Sporing held a (german) speech “Die E-Rechnung in Industrie und Handel” how Coop introduced ZUGFeRD and that and how it was certified by the authorities


For further details on all European countries please refer to the “EU compendium on e-invoicing retention” which also lists the legal requirements for the different countries and the (german) collection on legal foundations for electronic invoices in the EU (Sammlung der Rechtsgrundlagen für elektronische Rechnungen in der EG) and in particular interesting regarding B2G the CEFDIGITAL E-invoicing situation per country

German Situation


In August 2018 there was a 1h (english) speech on the 13th Froscon outlining the situation. Feel free to have a look at the slides and/or the video recording:

As defined in the german e-invoice law (amended E-Rechnungsgesetz in Bgbl 19/2017) and the according act, the E-Rechnungsverordnung, structured e-invoices will become mandatory vis á vis the authorities as of November 2020 in Germany.

All European formats providing the according attributes are allowed but the first german “country version” (i.e. CIUS) was the XRechnung, now also ZUGFeRD’s EN16931 profile is listed.

According to the justification for the e-Rechnungsverordnung the authorities receive an annual total of 7.95 million invoices, of which they expects 80% (6.36 million invoices) to become electronical.

The justification refers to the Architekturkonzept e-Rechnung, which estimates (page 96) 8 million invoices, half of which are direct and the other half are vis á vis the administration. Other sources talk about an expected 300,000 directly affected suppliers.

The official justification further expects a reduction of the processing time from 22,6 minutes to 11,78 minutes each and total savings of up to 62.38 million Euro for the government along with savings of 10.87 million Euro for the industry. The costs are expected to amount to 6.1 million Euro as a one off investment and 1.125 million Euro annually.

These 62.38 million is quite a lot but still much less than the 500 million expected in e.g. the Billentis E-invoicing business case, whichs says (page 21), “The difference to the total “public sector saving potential” above [in that case 6500-2600-3400] is the saving potential for the federal administration.”). The business cases also mentions a total “Minimum public sector saving potential” of 6.5 billion Euro per year just for Germany.


The german GOBD impose some obligations if you “save” an invoice in „the file-system“ – or if you accept (i.e. pay) structured or unstructured electronic invoices.

Among the most important duties is that both sender and recipient have to electronically archive the document in an unalterable way (“revisionssicher”), which requires (among others) tamper-free storage and a documentation of the process. BITKOMs has summarized the 10 most important requirements (german) and also published a exhaustive list of requirements vis á vis document management systems (in german).

On Youtube you will find a 20 minute german speech from 2016 on electronic invoices for SME.

In general, scanned paper invoices may be disposed, but only after certain criteria are met: e.g. it is defined who is responsible for that particular scan, the according person checked that its complete and legible, and the first digital backup has been created.

There is a (german) sample documentation on how to scan and how to file (also german). The DATEV has confirmed (in german) that digital files can be legally compliant.

In Germany there is no legal requirement to ask the recipient for permission to send her electronic invoices, if the invoice is accepted and paid, it means the the recipient also complies to the additional regulations. It is, however, her right to reject the electronic version and explicitly ask for a paper copy. In this case the paper original probably has to be provided without additional cost.


Further reading