title_body: what fonts to use for Adobe DE app on mobile devices? I am testing an epub file which I rolled up on my own. (I.e., I didn't use InDesign). 
  
  I deliberately did not specify a font for my ebook because the major ebook readers include their own fonts (or use system fonts). (Also, btw, it is very difficult to keep up with what readers use what fonts). 
  
  As it happens, I did include an embedded font for a special bit of content (it was a handwritten font), but that was only one part of the epub file. 
  
  I have tested the epub file on ibooks and Google Play. Everything renders perfectly. I can choose from about 8-10 different fonts on every epub reading software I have. 
  
  I tested the epub file on Adobe DE app  on Android. Everything looks good, except that there are no ways to choose font! ADE doesn't give you any information about what fonts are being used here (although you can change size).
  
  What's going on here? Does DE want to force publishers to use embedded fonts? Does DE secretly have a few dozen fonts inside the mobile app? Or is DE deliberately stripped down to allow ebook  distributors to provide their own fonts on their reading apps? 
  
  Are there any DE fonts which are on every platform? i.e. , common fonts like Georgia, Helvetica, Verdana, etc
  
  I would hate to be forced to dump an .otf font into my ebook file just because the reader just doesn't support any natively. Do you have any recommendations?
  
  UPDATE: Can I assume that ADE just applies serif and sans-serif to all content inside an epub file? Does DE have an algorithm for determining which html elements to apply a sans-serif font to?
upvoted_answer: I use ADE for basic testing for years and must say it is not the best tool on the market. The problem is its development is rather hectic and releases are often a bit unstable, full of tiny but annoying bugs. As for fonts, you are right with the default serif/sans-serif fonts. It depends on the rendering engine―try to display the same file from the ePub in IE, Safari and Firefox or Chrome and compare the results to the ADE defaults. It is always a good practice to choose what font to use in general, if not in particular, e.g. font-family: serif, Hoefler Text;.
  
  UPDATE
  
  If you are asking whether ADE has its own built in font, no, it hasn’t. ADE is installable for Mac and Win only, which means it uses default Win and Mac fonts according to default settings for its renderer. If you wish to know which font is used for which tag, the only one way is to test it or check the source code for the renderer.