ZUGFeRD
ZUGFeRD is a German hybrid e-invoice format that embeds structured EN 16931 data inside a normal PDF/A file, so the same document is both human-readable and machine-readable.
A ZUGFeRD file looks like an ordinary PDF to a person, but carries a full CII data set inside. Whoever receives it can read it like any invoice or extract the structured data automatically, whichever suits their system.
This hybrid design is why ZUGFeRD is popular for smaller suppliers: they can keep sending a PDF while satisfying e-invoice requirements. The French Factur-X format is technically the same specification.
Cortena reads the embedded data from ZUGFeRD files rather than running OCR on the picture.