title_body: what fonts to use for Adobe DE app on mobile devices?
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.