Free Chess Ebooks
I made a chess eBook Reader that makes chess PDF books interactive: https://ebook.chessvision.ai/
It works as follows: open a PDF book, send it to analysis just the first time, once finished, double-click on any chess diagram in the book, and explore it on the analysis board.
Here are five chess books that are out of copyright and may be downloaded legally for FREE:
https://chessuniversity.com/free-chess-ebooks/
Enjoy!