External links for e-Books are provided here
Pdf drive : https://www.pdfdrive.com/
Free ebooks : https://www.free-ebooks.net/
e-library : http://e-library.net/free-ebook.htm
Open library : https://openlibrary.org/
Wikibooks : https://en.wikibooks.org/wiki/Main_Page
Slideshare : https://www.slideshare.net/