You do need to show the title so that the user is aware of which article or book he is reading.
The kindle app shows the title of the book and on tap shows additional options

The ibooks app by default shows the title of the book and also the options available

My suggestion would be to use the space occupied by the app name to show the title of the document\article as the users would be aware of which app they are using but they might have multiple documents inside the app and unless they can see the title, it might not be too obvious which article is the opened article (imagine a case in which you are reading something and step away for a couple of hours and you have a lot of similar articles, so in that case the title will be very useful)