Unable to add books to my Books library on macOS Sonoma 14.7.2

I read a long list of similar threads here, I did a reset of 'online content', doesn't help.

I get:

Importing 0 of1. Failed: 0

or

Importing 0 of1. Failed: 1

The files (on internal drive) are perfectly readable with other software as Apples Preview (pdfs)...

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