Zip Files
Kindle
Epub-iPad
Calibre and Sigil
Contributions
Zip Files
The downloadable bundles are zipped. After download, just unzip, and the book will be ready to transfer to either your Kindle or your iPad. You will find the files, epub and mobi, in the inner folder. A good Open Source program for unzipping files is 7-Zip.
Kindle
It seems Mobi documents are obsolete. There are now two ways to sideload books that you currently own (whether acquired from Amazon or elsewhere). They both use the Epub format.
The first method is to upload (drag and drop) your book to your Send to Kindle page (amazon.com/sendtokindle). When it goes through, the book will appear in the library on your (online) Kindle and on your own personal Kindle Digital Content page. After your online upload, the book will remain on your Kindle, even when you go off line.
Tip: If your Epub book fails to go through, run it through a Calibre conversion Epub to Epub and the new copy should work fine.
The second method is to email your Epub file to yourself. Open Your account on your Kindle (Settings). At the very bottom is Send-to-Kindle email. Here you will find your own personal Kindle email address. Just send the Epub document/book to this address on a (blank) email and it should appear on both your Kindle and on your content page.
You can still sideload Mobi files directly on to your Kindle (by placing them in the documents folder). But sooner or later (most likely when you connect to Amazon) they will disappear.
Epub-iPad
There are currently two ways to transfer epub files to the app Books. 1) Using iTunes: Attach your iPad (or iPhone) to iTunes on your computer. Drag (transfer) the unzipped epub file directly to the iTunes-folder Books on your device. 2) Download the zip-file bundle directly to your iPad (or iPhone) from this site. It will appear in the Files app. Click the downloaded zip file, then click on the epub file. It will appear and be saved in the Books app.
Calibre and Sigil
You can easily convert eBooks from one format to another with the program Calibre. It also contains an eBook reader for your computer and many additional tools for formatting eBooks. If you use an eBook reader that has a different format from epub or mobi, Calibre can, almost instantaneously, convert the file. Calibre is a free and legal Open Source program created by Kovid Goyal. Please contribute to support Kovid’s endeavors.
Sigil is a fantastic tool for editing eBooks directly in the format you have converted to. It too contains an eBook reader. Sigil is a free and legal Open Source program. Please contribute to support the endeavors of John Schember.