[DiapDealer]

InDesign is probably defaulting to obfuscating/encrypting any embedded fonts when exporting to epub. That's what it used to do, anyway. And although, Sigil is perfectly capable of displaying those obfuscated/encrypted fonts, Kindle Publishing Guidelines specify that embedded fonts must not be obfuscated in the epubs being used to create Kindlebooks. Amazon adds their own obfuscation to fonts embedded in their books.

So in short ... this is not a Sigil bug. This is the fault of InDesign not allowing epubs to be saved with non-obfuscated, embedded fonts (or it wouldn't last time I checked, anyway).

So in essence, what you're doing is deleting the obfuscated fonts from the epub and then correctly re-adding the non-obfuscated ones. That's one way of working around the InDesign issue. There is another way.

Sigil is capable of unobfuscating (and obfuscating) fonts that are encrypted with the standard Adobe or IDPF font obfuscation algorithms. Right-click on any font-file in Sigil's Book Browser and see what is set in the Font Obfuscation submenu of the context menu. If either the Adobe or IDPF obfuscation is checked, then you should be able to select "None" to remove the obfuscation. Save the epub. You should now be able to use KindlePreviewer to view/convert your epub with embedded fonts.

Just realize that you may not have a legal right to redistribute the fonts you've embedded via InDesign--obfuscated or not. Always check the font license to see if you can legally distribute it with your ebook.