If you have the book opened in Adobe Reader, there is a function called Read Out Loud. You must first enable it under the menu View > Read Out Loud, and then you can go back to the same menu and choose whether you want a single page or the entire book read out. On YouTube, there are instructions for speech synthesis in the English version of Adobe Reader: How to make speech pdf Adobe reader for free
The speech synthesis and accompanying reader voice used depend on the operating system. I.e. whether the computer has Windows, Mac, Linux etc. In Windows 7, the speech synthesiser is called Microsoft Anna, which is only available in English. In Mac (Snow) Leopard, there are several alternative voices, both male and female. In Linux there are various speech synthesisers like espeak and gspeaker.
Adobe Digital Editions
Books read in Adobe Digital Editions (ADE), such as downloaded books from Ebook Central, cannot be read aloud because ADE does not have the same Read Out Loud function as Adobe Reader.
Speech synthesis for iOS (iPhone och iPad) and Android
Here you can find a YouTube video showing Android: Text to speech on Android, Samsung Galaxy S II and here you can find an app for iPhone and iPad: Speak it! text to speech application for iPhone and iPad.