Could you please tell what Operating System you have-Windows/Mac?
Are you using Export PDF services in Adobe Reader or in Web Browser like Google Chrome/Internet Explorer?
Try to export pdf by visiting this link - https://cloud.acrobat.com/exportpdf
Assuming, you are using Reader for Export PDF services,Try to first logout from the application by clicking on top right corner of the screen and then click sign out,close Reader and then launch it again, login into your account and then try to export to pdf.
Visit this link on how to use Adobe PDF Export services :How to Use Adobe PDF Pack
Let us know about the results.