I have a Kindle book with a deviating font, can I change it to normal?
You cannot change the font on some books if it's using an older format.


  Because those books are older topaz format instead of newer AZW
  format. You can't change the font type with the topaz format, although
  you can still change the font size. If you look at the content of
  Kindle with your computer, you will notice that the books with the
  older topaz format has .tpz extension while the newer AZW format has
  .AZW extension.