The enhanced typesettings engine improves the way Kindle books are formatted. Added support for the enhanced typesetting books.The Kindle for PC/Mac 1.19 has three major improvements: Amazon updated their desktop reading app Kindle for PC and Kindle for Mac to version 1.19, it is a big step as the last major version 1.17 was released several months ago. First thing, make sure to go to Tools Options and turn off automatic updates! Another way to get AZW files instead of KFX is to use the “Download & transfer via USB” option from the Manage Your Content and Device page at Amazon, but this only works if you have an E Ink Kindle registered to your account. Launch it and check that the option to automatically install updates is still turned off. Install the downloaded Kindle for PC version 1.17.
It is safest to use the link in this post to download it directly from Amazon, instead of going to a third party site.