If the website isn’t a known publisher (like McGraw-Hill) or a library with authentication (like your college login), it’s almost certainly pirated. Legal PDFs never come from “mediafire.com” or “drive.google.com” open links.
Under Indian copyright law (Section 52), fair use allows a single chapter or 10% of a book (whichever is less) for research or teaching. Photocopying the entire book is illegal. Singh And Sapre Communication System Pdf Free Download