Although the Amazon store has millions of books, it does not have everything. If you have downloaded eBooks from the web, import EPUB books into Amazon Kindle app on your phone for reading.
There are dozens of eBook file formats, although not all of them are commonly used. Some require specific eBook readers or other software to access them, or they must be converted to a more common file format before they can be used.
One of the more common eBook file formats is EPUB (Wikipedia EPUB technical explanation), files with the .epub extension, and it is an open XML-based format that uses open standards maintained by the Digital Publishing Forum.
EPUB has support from some of the biggest companies and software. Create a document in Google Docs for example, and you can download it as a .epub file that can be read in eBook reader apps.
Authors with multiple books will sometimes offer one for free, as a sample, or in return for signing up to their mailing list. The books are almost always offered in EPUB format and I have around a dozen eBooks, mostly downloaded from Facebook. I get a lot of ebook ads appearing in my Facebook feed and can grab the EPUB file and read it later.
How do you read EPUB files?
The .epub file format has wide support and if you download one and save it on your phone, you can simply tap it to read it. On an Android Phone it is automatically imported into Google Play Books, and on an iPhone it is automatically imported into Apple Books. It could not be simpler.
Those eBook readers have their fans, but some people prefer to use the Amazon Kindle app on their phone and it is available on iOS and Android. I you prefer it, you can import an EPUB book into the Amazon Kindle app.
There are a couple of reasons you might want to do this and one is that eBooks in the phone app are synced to all your devices, including a Kindle reader device if you have one. Using the phone app to import .epub files is an easy way to get them onto your Kindle. The Amazon Kindle phone apps also have a lot of good features and are easier on my eyes than Apple Books, for example.
The process of importing .epub files into the Amazon Kindle phone app is the same on iPhones and Android phones, although there are differences in the menus. Let’s look at Android first.
Import EPUB books into Amazon Kindle on Android
1: Where are your EPUB files?

My EPUB files are stored on Microsoft OneDrive, and I saved them when I was on a computer. This makes things a bit more complicated and you may skip this step and the next if your .epub files are elsewhere.
This is the OneDrive app on an Android phone. Press the three dots to the right of a .epub file to show a menu of actions.
2: Download the EPUB file

I am going to download this EPUB file on OneDrive to the Downloads folder on my Android phone. Alternatively, if you are browsing the web and come across an EPUB book, you could download it from there. Once it is downloaded, we can then do things with it.
3: Share downloaded files

Go to the app library and open My Files. Press Downloads and the contents of the Downloads folder is displayed. I am using a Samsung Android phone and it may be different if you are using a different phone. However, there will be some way of viewing downloaded files or files on the phone. Look for it.
Press and hold the downloaded .epub file. It is selected and a toolbar appears at the bottom of the screen. Press the Share button.
4: Send the EBOOK to Kindle

The latest version of the Amazon Kindle app adds a Kindle, Send to Kindle, icon in the Share options. You might need to swipe left or right over the icons or pull up the panel to see it. Press it to send this EPUB file to the app.
5: Add the EPUB to your library

You are asked what device you want to send the EBOOK to. It does not matter which you choose as long as the option at the bottom is ticked too, Archive in your Kindle library. The book is added to your Kindle library which is then synced to all of your devices. Tap Send.
6: EPUB books in your Kindle library

Here is the imported EPUB book in my Kindle library. It does not appear instantly and it takes a minute or more. First, there is nothing. Then a generic book/file icon appears. Tap the icon to open the book. Return to the library and that generic icon is replaced by the proper book cover. You are now ready to read it.
Import EPUB books into Amazon Kindle on iPhone
1: Where are your EPUB files?

As before, the EPUB files are stored in OneDrive, but you can browse your OneDrive online storage using the Apple Files app. Simply tap a .epub file to automatically import it into the Apple Books app. However, we want to import it into the Amazon Kindle app, so don’t press it.
Files can be stored on iCloud, OneDrive, or any other place the Files app has access to.
2: File actions

Press and hold the EPUB file until a menu appears. The action we want is Share. Press it to see the options.
3: iPhone sharing options

The usual iOS share options panel appears on the iPhone. Swipe over the row of apps. If you see the Amazon Kindle icon then press it. If the Amazon Kindle icon is not there then press the last icon, More, and then select it from the full list of apps that appears. To import an EPUB file to Amazon Kindle, you select it as a share option.
4: Fill in the form

This little form appears. The title was fine, but I found that the Author Name box was empty and this prevented the EPUB book from being imported. I had to type the author name into the box before tapping Send. What if you don’t know the author’s name? I guess any name will do and you just need to enter something into the box so it is not empty.
Make sure the Add to your library switch is turned on and then tap Send.
5: EPUB files in the iOS Amazon Kindle app

Here you can see the EPUB book in the Amazon Kindle library in the app. It does not appear instantly, so be patient and wait a minute. A generic book/file icon appears, but when the book is opened by tapping it, the proper cover appears in the Kindle library.
You can also see the book I imported on my Android phone too. Imported EPUB files appear on all devices, so if you have a Kindle, they will appear on that too.