You can try searching for the book titles or keywords like "IIT JEE books pdf" or "IIT JEE mathematics pdf" on Google. This might lead you to websites that offer free PDFs or links to Google Drive.
MHRD’s digital platform offers free video lectures and e-books for IIT JEE preparation. iit jee books pdf google drive free
For JEE Mains, are non-negotiable. You can legally download every NCERT book (Class 11 & 12) for free from the official website. You can try searching for the book titles