You can download e-books from various platforms, including:

1. Official Websites – Many universities and institutions provide free e-books.

2. Online Libraries – Websites like Google Books, Open Library, and Project Gutenberg offer free e-books.

3. E-learning Platforms – Platforms like Coursera, Udemy, and NPTEL provide study materials.

4. University Portals – If you're a student, check your university’s digital library.

Make sure to use trusted sources to avoid piracy issues.