Embedding XML?

[IngwiePhoenix]

Long story short; for a school project, I want to generate bills and invoices. Here in germany, a company may provide an XRechnung (aka. "ZUGPFERD") which is a PDF with an embedded, schemaful XML document.

I browsed the docs but saw no method to grab the underlying PDF generator to possibly facilitate that. But perhaps I just overlooked it...

Got an idea? Thank you!