What exactly happens when you try? If there is a message please tell us the whole text.
I have checked your account and it seems to be fine.
As it is not allowing you to convert PDFs, please try to sign out of the application.
Then relaunch the application and try to sign in again. Check if you are able to export files or not.
Check and let us know if you can export files or not.
If the issue still persists, let us know what exactly happens when you try to export PDF.
If you get any error message, please share the exact error message.
Also, try to export PDF online here: https://cloud.acrobat.com/exportpdf
Let us know if you experience any issue.
Are you using the ExportPDF service from within the free Adobe Reader? In my experience, that is very unreliable. Chances are that it will work when you use Meenakshi's suggestion to upload your document directly to the service via the link provided, start the conversion and then download the resulting document.