Documents to Books

Hi,

I'm a fresh owner of PaperWhite 3 (2015, Wifi) device with firmware 5.8.2 installed. I successfully sent few books using amazon email to it. However they reside as "Personal Documents" and not books.

I would like to organize these books using Calibre bat I can't find info how to move them from "Personal Documents" to "Books".

Is it possible to move/edit them to appear in Books section and organize them in Library?

Thanks for any help.