Notes for sideloaded material?

Question

I see

Indeed. I forgot to mention that it doesn’t work on sideloaded content, or even stuff that you’ve sent to your Kindle through Amazon. You can get Page Flip to work with sideloaded content, however, if it’s converted to KFX with a Calibre plugin.

http://blog.the-ebook-reader.com/2016/07/03/kindles-can-now-send-notes-and-highlights-directly-to-your-email/

How is that accomplished?

Installing and using Calibre is assumed. The e-book was converted to mobi.