ZUGFeRD and XRechnung:
Just what you need.

Since late 2013 a tool has been available for the automated and semi-automated processing of invoices, called ZUGFeRD (Zentraler User Guide des Forums elektronische Rechnung Deutschland). This format is based on the specifications of the European standardization program CEN, and offers multiple advantages. The PDF file can be viewed and edited on screen, and the embedded XML file is the basis for automatic further processing. Invoicing processes are leaner, and there is no need for the invoicing and invoiced parties to coordinate between their billing systems.

Since April 2020, the XRechnung format has been standard in public administration for electronic invoicing. Here as well, stratEDI offers help with implementing the format, for smoother public-sector transactions.