KF-PDF-A3: The document does not declare itself as PDF/A-3
This code shows up when an electronic invoice is validated. Here is what it means, why it fires, and what to change in the file.
Why this code appears
The XMP metadata does not carry pdfaid:part = 3. Factur-X requires a PDF/A-3 container: it is what guarantees the invoice stays readable and self-contained for the legal retention period.
How to fix it
Export the PDF as PDF/A-3 (level B is enough) and check that the XMP carries pdfaid:part and pdfaid:conformance. A plain PDF with an attachment added does not become a PDF/A-3.
Where it happens
This check is ours, not a code from the standard: we do not cover enough of EN 16931 to borrow its numbers, and a misattributed official code would send you to fix the wrong field. It concerns PDF.