Check the table below for a comparison of reading apps based on features they support.
|Acrobat Reader||Documents by Readdle||Dropbox||iBooks||Kindle||Play Books|
|Copy text to clipboard||Y||PDF only||Y||Y||Y||Y|
|Dictionary lookup||Y||PDF only||Y||Y||Kindle books only||Y|
|Google Play store app||Y||N||Y||N||Y||Y|
|Export books to other apps||Y||Y||Y||N||N||N|
|Highlights and notes||Y||PDF only||N||EPUB only||Kindle books only||Y|
|Sync highlights and notes to cloud||Y||N||N||iTunes books only||Kindle books only||Y|
|Share highlights to social networks||N||N||N||Y||Kindle books only||N|
|iPhone or iPod Touch support||Y||Y||Y||Y||Y||Y|
|Night view||Y||Low contrast||N||EPUB only||MOBI only||Y|
|Open books from other apps||Y||Y||Y||Y||Y||N|
|Open books from cloud storage||N||Y||N||N||N||Google Play only|
|Y||Y||Y||PDF only||PDF only||N|
|Sync offline books to the cloud||acrobat.com only||Y||dropbox.com only||N||N||N|
|Search in a book||Y||Y||Y||Y||Kindle books only||Y|
|Sync last position read between devices||Y||N||N||iTunes books only||Kindle books only||Y|
Books have a copy quota
Last updated on July 21, 2013
Adobe Reader supports the most features. If it had EPUB format support it would be unbeatable.
Documents by Readdle has the best cloud integration. It is an indispensable app to have if you store your books in the cloud. Its reading features lack polish. Night view is low contrast, making reading very difficult. EPUB support is buggy. It does support other media formats besides books.
Readdle is another competent reading app. It is very polished and has one feature that no other app has so far. It tracks your reading time, and tells you how much time you have left to finish the book. The only significant feature missing is search.
If you have an Android device and want cross-platform support, Adobe Reader seems to be the best option, but PDF books are unwieldy on small screens.
Kindle is my favorite for reading on small screens. I read most novels on a smartphone. I wish the app had better PDF support - search, copy text to clipboard, highlights and notes, and night view.
At the end of the day, I wish all books were DRM-free and I could read them in the best app du jour.