Find eBooks, PDF Files with OpenPDF
Finding PDF files using Google is not a new trick and many people use that to look for PDF files they want. But a search engine specifically for this job is always better.
OpenPDF is a search engine for finding/searching PDF files available publicly online. There is nothing much to explain in as you just have to type in your query in the search box and hit Enter.
They also have a toolbar for Firefox from where you could quickly search for PDF files without going to the website.
Find PDF files with OpenPDF.com!