Make a search for the word motor in a DWF and see what can be found.
Because DWF files can now be indexed and returned by leading search engines, designers can be confident that others can access and experience data-rich information online, improving collaboration and communication.
Autodesk says users can search by file type and find pages that are CAD documents posted online. To locate a drawing, map, or model, users construct a search including the phrase “Filetype:dwf” and terms regarding the type of file sought.
Notice that you cannot use Filetype:dwf as the article says. You must use filetype:dwf with lower case to have it work. Wondering when DWFx will be supported.
In the Google advanced search it's also available among the File Formats for easy access.