Thank you so much. You already solved my problem!
I used the Sensei Media Attachment Plugin to attach my PDF’s.
Now I am simply using Gutenbergs Data Block and it works fine.
I also noticed, that all Sensei-settings have a decent delay until they show up on my live page. That have been the reason for many confusions. Now I know that I always have to wait 1-3 Minutes before I check results. Is that normal?
Best,
Gregor
