Hello Heinz-jürgenk,
As per the description above, you are not able to login to your iPad as your credentials are not working and it's asking for PUK code, Is that correct?
You have to contact your cellular service provider or Apple support as the PUK error is related to Handset/Sim Blocked issue. To get the PUK, contact the Apple support or Cellular Service support.
If you are not able to login in mobile application Adobe Reader DC with your current Adobe ID and password, then please uninstall and reinstall Adobe Reader from AppStore. For sign-in issue, you may refer to Adobe ID account and sign-in troubleshooting
Feel free to update this discussion in case you need further assistance related to Adobe Reader DC.
Regards,
Anand Sri.
(Edited response.)