You can try this app for free at http://doc.endlessparentheses.com
This app contains a convenient list of ALL built-in functions and variables contained in Emacs. Just tap one of them and you'll be sent to its documentation at http://doc.endlessparentheses.com
There are 2 ways of visiting a function's (or variable's) documentation: - You can search for a function straight from the app. - You can select the function's name when reading it somewhere else (like the browser) and share it to Emacs Documentation.
** Permissions The ONLY permission required is internet access, so that it can access the online documentations. If you're the suspicious type, the app is open-source, so you can find it on https://github.com/Bruce-Connor/emacs-documentation-android/
Optional built-in viewer for documentation. Saves your zoom preference so you don't have to zoom in every time.
Light theme (change the theme in the settings menu).