The ExportPDF function can be accessed via different paths: Either with the functionality build into Adobe Reader, or via the web interface directrly. I assume you are trying to do it via Adobe Reader. Is it possible that you are not logged into your Adobe account on the Reade? Or, logged into a different Adobe account from the one that has the subscription? You can always try to use the web interface directly: Go to https://documentcloud.adobe.com/link/acrobat/export-pdf and upload your PDF file. You can then download the resulting Word document.