It is possible to “side-load” books into the Box of Books Offline Reader. This allows you to read your own books within the offline readers. Our readers accepts .pdf and .epub files. This guide will show you how to side-load books into the MacOS readers.
Open Box of Books reader and go to File > Add to Library (alternatively, press ⌘-O); a window will pop-up promoting you to select the book you wish to side-load.
Select the book (pdf/epub format) and click ‘Add’; the book will be added to your reader’s library/bookshelves.
& that’s it, enjoy your reading your book(s)!