A file with the .MOBI extension is used for storing eBooks. It was originally a Mobipocket Reader format, but has since been adopted by several readers as well. Amazon bought Mobipocket in 2005 and subsequently discontinued the MOBI format in 2011.
What is a MOBI file?
The current Kindle formats (AZW3, KF8 and KFX) are based on MOBI and is a proprietary format used exclusively on Kindle devices. And, in fact, you can still open files with the MOBI format directly on your Kindle – you just have to send them to your Kindle first.
How do I open one?
Since MOBI is an eBook format, most free desktop eReader programs support opening and viewing, such as Caliber, FBReader, Mobipocket Reader, or Mobi File Reader, to name a few.
Once you’ve downloaded and installed one of the free applications, opening any of your MOBI files is relatively easy. For Caliber, all you have to do is click on the “Add Books” button, then choose one of the options shown in the image below.
How do I convert one?
Just like any other file format, you need specialized software to handle the conversion of MOBI to a different format. If you simply try to change the extension, you may end up with a corrupt and unusable file.
Besides being an eReader, Caliber comes with a handy conversion tool that can convert any of your eBooks into 16 different formats.
If you don’t want to download a third-party application to convert your files, there are a couple of great online converters that allow for conversion to some of the more popular formats, such as ePUB, PDF, FB2, and LRF. This is probably one of the fastest ways, as you don’t need to download any software and wait for it to install.