Quote Originally Posted by MarcT View Post

Transparency already are supported in PDF...
but not in the PDF/X series up to now

here is a link to PDFA.org description, and a quote:

https://www.pdfa.org/wp-content/uplo...a-Nutshell.pdf

In addition, PDF/X-4 allows the use of transparency, a PDF 1.4 feature forbidden in PDF/X until PDF/X-4.