Adobe PDF Pack and Adobe Acrobat DC both are part of Document Cloud family. However, the subscription for PDF services might not let you to directly convert it to Adobe Acrobat DC. You need to cancel the current PDF Pack subscription and purchase Acrobat DC.
You can refer to the Adobe account and try the steps suggested here Upgrade or change your Creative Cloud plan and if it doesn't let you to upgrade the plan.
You can refer to the cancellation steps here and cancel the current subscription- Cancel your membership or subscription | Adobe Acrobat, Document Cloud PDF services
And then buy the Acrobat DC from here- Plans and pricing | Adobe Acrobat DC
For any further assistance, you can contact to our billing support team- Contact Customer Care