This article explains how to sync books on your iPad. Instructions apply to Windows and macOS. Only certain eBook formats are supported by the iPad. If a book is in a format that is not supported by the device, convert it to a different file format.
The easiest way to add books to your iPad is through iTunes, especially if you use your computer to sync content with your iPad.
To do this, add books to iTunes. For Windows, open iTunes and drag the e-books to the On My Device section. For Mac, open the Books application and drag the e-books to Books.
Then sync your iPad with iTunes to copy the books to your iPad. The books will be downloaded to the Books app, in the Library section.