Hey Riccardog,
Sorry to hear about the frustrating experience. As support for the Export PDF service is only available on the forum, that is the reason you have been redirected here.
Follow the steps mentioned below, to activate the subscription-
1- Export PDF is an online service that you can use online via: https://cloud.acrobat.com/exportpdf
Sign Out & Sign In if you have already signed in.
2- You can also use the services through free desktop 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 Export PDF service, you may refer to- Using Adobe Export PDF
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 does not work.
Regards,
Akanchha