The PDF is password protected — the embedded e-invoice cannot be read. PDF/A-3 (the basis of ZUGFeRD/Factur-X) forbids encryption.
Generate the invoice without password protection, or remove the encryption and re-export as PDF/A-3.
The Billhorse validator checks XRechnung, ZUGFeRD and Factur-X right in your browser — your file is never uploaded.
Open the validator ← All validation rules
Rule source: EN 16931 / XRechnung (KOSIT) or Billhorse check (BH-*).