Instead just indexing the web pages, the search engines also indexes various file-formats, e.g. PDF Files, PPT Files, DOC Files, etc.
The following method is the most easiest method to get the search results from relevant file formats. filetype: [format_name] [your_query]
Lets say, if you want to get the search results for Microsoft Help and only look into the .doc file formats, then, you will have to enter the query as, filetype:doc Microsoft Help
Note : The pictures displayed here on Google, but you can search and try them all on Bing as well. If they would be having the relevant results, then of course, results will be shown.
If you want to get the search results for Microsoft Help and only look into the .pdf document file formats, then,
you will have to enter the query as, filetype:pdf Microsoft Help
If you want to get the search results for Microsoft research and only look into the .ppt document file formats, then, you will have to enter the query as, filetype:ppt Microsoft research
This tricks works for most of the file formats, for example doc, docx, xls, xlsx, ppt, pptx, txt, rtf, zip, pdf, most image, audio and video formats.
Hope it helps.
Enjoy!