You want to read a PDF file on a tablet or a mobile phone? To automatically adjust the text size on the screen of your device, it is better to use the ePub file format. ePub is a free and open e-book standard by the International Digital Publishing Forum with extension .epub. ePub is designed for reflowable content, meaning that the text display can be optimized for the particular display device used by the reader of the EPUB-formatted book. With the free tool called Calibre you can convert your PDF eBooks in ePub format and in this tutorial I will show you how.