Known failure in V4.70. Use drag and drop which does work.

"You can drag messages from any folder window to any addressbook (even minimized) and Pegasus Mail will create an addressbook entry based on the information in the message."

Problem is on the list and may get fixed for the v4.71 release which is already planned to address some  other issues including one or two with new spelling checker.

Hello

When I try to add a new email address by right-clicking on it and selecting the third option (add address to a addressbook ...), and then choose one address book with "select" or double-clicking on it, nothing happens. The new address is nowhere in any address book.

Using PM 4.7 (english version) with Win 8.1 

Thanks

Luc