I have a purchased PDF Exporter and have changed computer. On my new computer, it doesn't work and I can't purchase a new one on the website.
It seems that you are using Adobe Acrobat Reader DC.
Please try to sign in with your Adobe ID in the application and then try to export PDF.
You can also export PDF online here: https://cloud.acrobat.com/exportpdf
Let us know if you have a different issue or you need nay help.