Hi Beancounter2,
Thanks for posting here.
Based on my research, I found that the following links as your reference:
"Either there is no default mail client or the current mail client cannot fulfill the messaging request" error message when you send e-mail from third-party program in Outlook: http://support.microsoft.com/kb/813745
Either there is no default mail client of the current mail client cannot fulfill the messaging request-----error Outlook 2010: http://social.technet.microsoft.com/Forums/en-US/outlook/thread/b8ce23ee-1408-45a6-96e9-b8f874798e0f/
Moreover, I would like to know the following information:
1. I would like to know if you will encounter the same issue when you open other files.
2. Do you mean that you encounter the above issue when you open the PDF file as an email’s attachment? Did you encounter the above issue when you open a standalone PDF file, not an attachment?
If you only encounter the issue when you open the PDF file, it may be related to Adobe, you can contact Adobe to see if they can help you resolve the issue.
Best Regards,
Anna Shi