Many of you already know that Autodesk's DWF file format is a registered file type on www.google.com, but I thought I mention it again anyway. That way, it remains fresh in our ever so overloaded brains and gives those, who do not know about it as yet, an opportunity to learn.
To cut the long story short - you can search specifically for DWF files with the Google search engine, when applying the following search syntax:
As an example, to return only Inventor related DWF you would apply the following syntax:
Doing so would return these results: http://www.google.com/search?hl=en&q=inventor+filetype%3Adwf
The same principle applies to other products such as "autocad filetype:dwf", "revit filetype:dwf", "civil 3d filetype:dwf" and so on.
I personally was amazed by the number of results when I learned about this DWF specific search first.