When the "Comment" menu is open, copy and paste are disabled, until the menu is closed. So in the process of adding mark ups and comments, you need to open the Comment menu to add a mark up, then close it to copy and paste to use that markup else where on that page or another, then re-open the comment menu, and continue back and forth.

The copy and paste option must be available with the comment menu open or the functionality of the program, which we use primarily to mark up and comment on pdf's, is totally lost.