Calibre is a eBook management library for the computer or ereader. The power of it comes from the plugins that helps to work with various file formats.
Calibre: Error communicating with device
Calibre: error communicating with device, failed to find obfuscation key is due to encrypted fonts. Calibre’s KoboTouchExtended plugin was unable to locate the key to decrypt the embedded fonts to convert the EPUB file to KEPUB.