Hi Michaela,
Sorry for the delay in response.
We see that there is an active subscription of "PDF Pack" registered to your account. Please ensure that you are using the correct application Adobe Reader DC not Adobe Acrobat DC. There is a possibility that you have used the trial for Acrobat and that isn't working with the current subscription.
2- If you have Acrobat DC installed, please uninstall it using cleaner tool- http://labs.adobe.com/downloads/acrobatcleaner.html and install Adobe Reader- Adobe Acrobat Reader DC Install for all versions
3- Check online through https://cloud.acrobat.com/ Sign Out and Sign In once.
Please refer to - How to Use Adobe PDF Pack
You may refer to the following link for any troubleshooting: Troubleshooting Create PDF, Export PDF, Adobe Send, Fill & Sign … services(PDFPack or Document Cloud Services).
Regards,
Akanchha