Originally Posted by tompe
Just use Calibre to upload the file and maybe specify that the format should be mobi. Worked for med with lit books I had imported to Calibre.
With modern versions of Android that unfortunately doesn't work, because newer Android devices don't mount as a drive, but as a "portable device", which Calibre can't recognize. You have to use some other method to get your books to the Kindle app, such as copying the files to the "Kindle" folder using Windows Explorer, using the Calibre server, or using Amazon's "Personal Documents" facility.