To convert a Kindle file, you need the .mobi or .azw file that the Kindle file contains. To do this, please go to your Amazon Account and select Manage Content and Devices ( . Select the book you would like to download and under Actions choose Download and Transfer via USB.  (You can choose your Kindle as the option.  You're not going to actually transfer it via usb, it's just the only way to download the file to your device.) Once you have the file, send it to the device you want to convert it on, and open it in the converter app.