How do I download the free Swift Programming Language book (Swift 5 Edition) from the Apple Books Store?
Assuming you are using iCloud Library for Apple Books, the location for the raw .epub files (can be accessed from the terminal.app) is:

/Users/&lt;YourUserName&gt;/Library/Mobile Documents/iCloud~com~apple~iBooks/Documents

As for opening books downloaded from Apple Book Store in Windows/Linux, the books are DRM protected (even the free ones).

Source:


http://apple.stackexchange.com/questions/296462/ddg#297650