I want to read a Microsoft Word document (
.docx format) on my Kindle Paperwhite, with its original two fonts (every third paragraph has a different font from the rest of the document). How do I do that?
I'm just speculating wildly here, but the first thing you need to do is to specify 2 fonts which you know for sure are supported on the Paperwhite.
Kindle Personal Documents Service does some strange things. I'm not sure if it even reads font information from MS Word. It certainly will not embed fonts automatically from MS Word.
However, if it is able to read and convert font(s) info from MS word, Here's a list of Kindle fonts you can choose from (which may or may not be out of date). http://www.paulsalvette.com/2012/06/embedding-fonts-in-kindle-ebooks.html
You can differentiate texts in other ways than fonts. For example, you can put it in italics or make the font size smaller. Generally it is frowned upon to use more than one font except on the heading.