You have used the trial version of Acrobat DC and subscribed for the Export PDF subscription. Export PDF is an online service which you can not use with the Acrobat DC application.
You may uninstall the Acrobat DC using the cleaner tool- Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs
And install the Adobe Reader DC desktop application Adobe Acrobat Reader DC Install for all versions
Or can use it online via- https://cloud.acrobat.com/exportpdf
Sign In with the same email under which you have the subscription registered.