It really isn't necessary. What I did way back when was simply create a re-usable Word 2007 template for creating PDFs designed for 6" eInk readers.

Set up the template by setting:

• Paper Size = 3.4" x 4.7" (play around until this looks right)
• Margins = 0.1" (or whatever looks best to you)
• Set up your fonts and font sizes for each style you use

That is pretty much it. It will take a little while to get the template tweaked for your tastes, but afterwards it is very quick and easy to apply it to a Word document. Then create your document in Word and save it. Then save the Word document as a PDF.

BTW, I cannot remember the paper size I used, but just play around with the dimensions until you get as little waste as possible.

EDIT: I think using a template the allows you to view the text in approximately the same size and configuration as the finished PDF will look on a Kindle is much better than simply converting a larger format document. It is sure easier when editing the document to get each page to display the way you want.