Using Google search you can search for a specific filetype instead of the content on webpages. You can restrict your search to Word document, a PDF file, a Powerpoint presentation or an excel workbook.
Offcourse when you want a cover letter or a resume template in the form of a word document, a presentation on agile methodology to senior leadership or a cricekt rulebook in the form of a PDF file, this is of an immense use. When you can search and get a specific document, suddenly, web content is not as much useful.
How do you search is as simple as it gets. Mention your query followed by filetype:doc, filetype:xls, filetype:ppt, filetype:pdf and more. Google support almost all the filetypes so long they are available.
I used to use the query string followed simply by '.doc', '.pdf' or something like that. It does return the results but not as precisely as 'filetype' does. It restricts the search to specific file types and returns you exactly what you asked for.
Ensure you form your query string appropriately followed by 'filetye:doc or whatever extension you are looking for. Note there is no space between filetype and the colon and the extension.
There is alternative way to filetype. You could use ext instead of filetype. For example ext:doc, ext:ppt, ext:pdf and so on. Both the 'filetype' and 'ext' shall fetch the exact same results.
I am fond of filetype but be certain that you could very well be using 'ext' after all it's short and that's the whole point.
Next time you want to perform a power search ensure, to use the filetype/ext when you need it.