If you spend a lot of time reading electronic documents then it may be worth giving your eyes a rest and let your mobile device do it for you. Apple's iOS has a built in feature for accessibility purposes that allows you to select a block of text (whether it is in an email, on a webpage or a PDF document) and you can then convert the text to speech. You can turn the text-to-speech (TTS) feature on in the accessibility area of the settings app. While this is useful it is limited as you have to manually select the text you want read, which can be a tricky process. Another option is to use an app that can read text automatically. Voice Dream is an app I have been using to read articles for me while I am driving. It costs $13 on the app store and comes standard with the built in iOS voice and one other voice. You can purchase additional voices that have a more natural intonation as well as US, British or Australian accents. These range in price from $3.74 to $6.49. There are a few free TTS alternative apps such as SpeakPad and Voice Generator, they also have the option to purchase additional voices.
For Android tablets there are several TTS apps. There is the built in Google TTS and if you have a Samsung device there is also the Samsung TTS. These can be configured under the Settings | Language and input menu. The built in engine is not supported by all apps but you can use it to read Google Play books. Ivona Text-To-Speech is a third party app that has more natural sounding voices and is currently in beta (so is free). Once again you can purchase additional voices in the app. Happy reading.