File Type Searches
Google has been indexing 14 file formats. PDF formatted files are the most popular after HTML files. PostScript and Microsoft Word, Microsoft PowerPoint files are also fairly common. The other file types are relatively uncommon by comparison.
- Adobe Portable Document Format (pdf)
- Adobe PostScript (ps)
- Lotus 1-2-3 (wk1, wk2, wk3, wk4, wk5, wki, wks, wku)
- Lotus WordPro (lwp)
- MacWrite (mw)
- Microsoft Excel (xls)
- Microsoft PowerPoint (ppt)
- Microsoft Word (doc)
- Microsoft Works (wks, wps, wdb)
- Microsoft Write (wri)
- Rich Text Format (rtf)
- Shockwave Flash (swf)
- Text (ans, txt)
You can limit your search to one or more file formats.
The query in the above examples limit to the file formats to pdf, ppt, and doc.
Adv Search form does not allow to include more than one file formats as given in the Example 3.
Further reading: http://www.philb.com/fileformat.htm
Note: This functionality is also available through Advanced Search page. Look at the following example: