From JW Manus:
I’ve been using Amazon’s Kindle Previewer app ever since I started formatting ebooks. Have to say, I was never much impressed with it. It had some useful features and it was a quick way to convert an epub file into a mobi file, and a sort of quick way to convert a Word doc into a mobi file so I could load it onto a Kindle or tablet. As for viewing a book on the computer? Forget it. It looked awful and the screen size couldn’t be adjusted. For some tasks it was essential, but I never fully trusted it to give me a hundred percent true rendering of my ebooks.
Then I got a brand new computer and when I downloaded the Kindle Previewer, I got the newest version.
And oh my God, Amazon, what have you done?
. . . .
For those of you, my dear readers, with a Do-It-Yourself frame of mind, this version also converts Word docs. No more need for converting the doc first in MobiPocket and then converting the prc file. Click File > Open Book and select a Word doc and the program will convert it into a mobi file. It won’t be a commercial quality ebook and it won’t build the internal navigation guide, but it does allow you to check your styling and the mobi file can be loaded onto your Kindle or tablet for proofreading.
Link to the rest at JW Manus