Hi Rendragon,
Adobe Export PDF service never ask for the the redemption code or serial number. We have looked into your account and found that you have used the Acrobat DC in past. You may uninstall the Acrobat DC for your convenience. Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs
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
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 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 doesn't work.
Regards,
Akanchha