With or without the PDF Pack subscription the "Combine Files" feature should be available in the Tools menu.
However, if you cant find it then try searching it manually.
You may try accessing your service online via web browser https://cloud.acrobat.com/exportpdf and see if you can access it directly from there or not?
If application doesn't show the "Combine PDF" then try uninstalling it using cleaner tool- Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs and install it through Adobe Acrobat Reader DC Install for all versions
Let us know if it still doesn't help.
This happened to me. There is no option to call Adobe or chat about this problem. I have seen a lot of posts about it. The advice in the box above does not work. Good luck. I'm looking for other software.
The "Document Cloud Services" https://cloud.acrobat.com/exportpdf site was down for a while and there was an intermittent issue going on. Which has affected few users and impacted their document cloud services (Exporting, Creating and Combing). This has been escalated to the concern team and they have been working on the resolution.
The issue has now been rectified and the services should be up and running fine by now.
Let us know if it hasn't resolved at your end.