Motivation:

You have an ebook with .epub or .mobi format in your MacBook or PC.
You want to put it into your iPhone or iPAD so that you can read it on the go.

Solution 1:

1. Upload your ebook to iCloud Drive.
2. Install Kindle or Apple Books or Google Play Books on your iPhone or iPAD.
3. Login your Kindle or Apple or Google account.
4. Open the Files app to go to iCloud Drive.
5. Open the ebook.
6. Tap the Share icon in the lower left hand corner.
7. Select Kindle or Open in iBooks or Play Books.

Solution for Google Play Books:

1. Install Google Play Books on your iPhone or iPAD..
2. Log in Google Play Book website using your Google account.
3. Upload your ebook in EPUB format to Google Play Book website.
4. Open Google Play Books on your iPhone or iPAD.