A little-known feature of iOS 9 is that it supports custom fonts, much like a Mac. You need either an app that supports installing them, like Ulysses for iOS (my favorite and only writing app now), or an app like AnyFont, a font manager.
Note that, in order to see your custom fonts, an app has to support them. I used Ulysses to install Museuo Sans, but I can’t set it as my default font in Safari or system-wide. Fortunately, it sounds like many apps have adopted iOS 9’s custom font features, including even Office for iOS.