Hi Bernard,
Turns out, there was already a bug raised in 2006(!): https://bugs.kde.org/show_bug.cgi?id=126942
thanks for finding this.
I've added links back to this mailing list thread - is there any way I am able to raise the profile of this ticket to get it looked at (beyond having this discussion)?
to be honest I think you need professional support for this. Overprint support is a bit exotic, and you are very unlikely to find a volunteer with the motivation, the time and the skills to implement this. In a previous email you mentioned that you write on behalf of a company. I strongly suggest that you ask them for money to hire one of the companies that offers professional Okular support. Best, Oliver
smime.p7s
Description: S/MIME Cryptographic Signature