To get PDFs, simply go to any search engine online of the many that are available. In your search results you are most likely to find two kinds of search results for the text that you are searching for in the PDF form - one where you have to buy the e-book, and another where you can read the book without having to buy it.
Unlike some libraries where you can access the text but not download it, a PDF by its very formatting can be downloaded. Also, you might find PDFs of similar texts displayed as similar search results on your webpage. E-books have gained immense popularity and account for the large sale of e-book hand readers.