Fabs

Was about to recommend Anna's Archive.  I respect their explicit and principled flouting copyright laws.  I wish them luck.

MarsIronPI

https://annas-archive.org/

https://libgen.rs/

 are my primary places to search these days. Other than your local library if they offer a program like Libby.

BooksAndArticles

Where can I get free eBooks?

https://annas-archive.org/ and https://libgen.rs/ are my primary places to search these days. Other than your local library if they offer a program like Libby.