I have Adobe Acrobat Pro DC, when I try to click on the mail (envelope) icon - I get an error that reads "An error occurred while trying to create a mail document. Adobe Acrobat is unable to complete your request. I am using Outlook on Mac (365). I never used to have issues doing this - it started about a month ago.
Sorry for the delayed response.
Are you still facing this issue? If yes, please try following troubleshooting steps:
1- Check if an update is available for Acrobat using "Check for updates" option under "Help" menu, reboot the machine after installing update and try again. You may also download updates from here: Adobe - Acrobat : For Macintosh
2- If step 2 doesn't work, try troubleshooting steps given here: Attach to email option is not working | Acrobat DC, Acrobat Reader DC
3- You may also try the steps suggested in this link by Barbara Adams: Error when using Outlook as default mail application in Acrobat DC (Sign and Send PDFs)