Regarding PDF copy of a book downloaded from reputed universities
If a reputed university has uploaded the PDFs online, chances are they are legally allowed to. This could be, for example, if:

The book's copyright has expired.
The copyright allows for distribution (e.g. if the book is open access).
The copyright holder allowed the book to be distributed.
The university paid for the right to distribute the book.

So it should be OK for you to use it. If you're still worried, look at the license statements that come with the download.