Google (the search engine) has a few tricks that not many users know about. For example, searching for pdf, .doc, .swf (flash) files on a website.
If you want to filter and get displayed as you search only the pdf files, write in Google, “site:website.com pdf”, without the quote marks.
Google will display the pdf files as the first results, there is also “[pdf]” mentioned in small text there on the left side of the title of the page.
If there are no PDF files, Google might display some results from that website that contain the word “pdf”.
The same can be done if you want to search for Microsoft Office documents (.doc). There might also be more file extensions that are supported. The main idea is that “site:website.com” will display all the pages indexed from “website.com” (this is an example).
Another trick is to see pages under a directory, for example http://website.com/directory/article1.html. If you go to http://website.com/directory/, you might get in your browser, a message saying “forbidden” (a server setting), or a blank page.
If you still want to see the other pages under that directory, go to Google and search for “site:http://website.com/directory”. If those pages are indexed, they will be displayed as search results under Google.
The idea is that you might not know what pages exists under that directory and this is a good way to find.