In the past and in most other Mac programmes we had one click to add a PDF to an email now it is three clicks. Many have raised this issue in the last 12 months. And there is a supposed patch via the PList but it does not work for me on the Mac have tried several times over the months.

https://helpx.adobe.com/acrobat/kb/send-email-attachment.html

This article did not fix it for me.