How to save PDF eBooks to iBooks on Your iPhone or iPad
How to Save From Apple Mail to iBooks
In the latest iOS version, following the steps in the above video only opens the ebook on Books (formerly iBooks). It doesn’t save it anymore.
To make sure it’s saved, please follow these two extra steps:
Tap on the screen once to show the menu. Tap the Share button.
A menu will appear at the bottom. Choose Copy to Books.