Hi Danb,
We're sorry for the trouble you had, what is the error message you are getting while sending a PDF file as an email attachment using Adobe Reader? Would you mind posting a screenshot of the error you get? To post a screenshot, refer to https://forums.adobe.com/docs/DOC-7043#jive_content_id_How_do_I_attach_a_screenshot
Make sure that you have the latest version of Adobe Reader installed, check for any pending updates from help>check for updates, reboot the machine after updating Adobe Reader.
Refer and try the suggestion from the following help article and see if that resolves the issue Attach to email option is not working | Acrobat DC, Acrobat Reader DC
You may also refer to How to use the email icon to directly send file as attachment
Are you on Mac or Windows machine and what is the version installed?
What is the version of Adobe Reader installed? To identify refer to Identify the product and its version for Acrobat and Reader DC
Let us know how it goes and update this discussion for any further assistance.
Thanks,
Anand Sri.