We use Outlook 2010 and Adobe Reader 11.0.2. Our users export a report from our ERP system which converts it to PDF and opens in Adobe Reader. Our users then need to use the "Send file as email" function.
If Outlook is open whilst doing this the envelope button simply greys out for a couple of minutes and then become available again. If Outlook is closed it opens a new Outlook email and attaches the file as expected.
I've tested this on various PC's and various versions, down to 9.5, of Adobe Reader with the same result.
If you first save the file the function works fine.