Okular - Okular is a universal document viewer based developed by KDE.
LibriVox Audio Books Supporter - LibriVox Audio Books Supporter app comes up with an extensive collection of audiobooks through which you can search for your favorite book and listen to it in your native language right at your fingertips.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Speechy - Speechy is an app by Twelve Stars Software that comes up with features to help you in reading text in a variety of different formats such as pdf, txt, EPUB, webpages, and many others.
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
FLOOX - FLOOX app allows you to select a book from the internal storage to listen to it in the audio version by selecting the desired text-to-speech settings.