Hey Annav,
We have looked into your account and found that you do have subscription for the Adobe PDF Pack. So there shouldn't be any trouble combining the pdf files.
You may check the following steps and see if that helps-
1- PDF Pack is an online service that you can use online via: https://cloud.acrobat.com/exportpdf
2- You can also use the services through free desktop version of Adobe Acrobat Reader DC: Adobe Acrobat Reader DC Install for all versions
3- “Sign In” using the email (Adobe ID) under which you have subscription registered.
4- For detailed description of how to use the PDF Pack service, you may 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).
Let us know if it still doesn't work.
Regards,
Akanchha