Searching Files with Google

So I'm searching for something on Google again. What I'm getting in search results are some useful pages, mostly HTML pages. And yes, there are some result links with [PDF] mark.
I realize these are PDF files stored on some websites which Google has indexed. I also realize that contents available on net in the form of PDF/ PPT/ DOC/ XLS files are better resources than ubiquitous HTML pages.
Now the question: Is there any way I can search those files, and restrict my search results to File URL only.
Yes, if I add "filetype:PDF" in Google search box after search string, I'll get PDF files in search results.
There is another option: Google allows you to create Custom Searches. Using this feature it is possible to create a Custom Search box, which will search only files.
Go to Google and try this. If you don't want to dig into technical details, I've created one for me. This is also available at the bottom of my blogs.

When I do a file search, only links with files are returned. In addition, the result page provide filter for PDF/ DOC/ XLS/ PPT files.

Check this and add my blogs to your Favorites :)