If you include filetype:suffix in your query, Google will restrict the results to pages whose names end in suffix. For example, [ web page evaluation checklist filetype:pdf ] will return Adobe Acrobat pdf files that match the terms "web," "page," "evaluation," and "checklist." You can restrict the results to pages whose names end with pdf and doc by using the OR operator, e.g. [ email security filetype:pdf OR filetype:doc].

When you don't specify a File Format in the Advanced Search Form or the filetype: operator, Google searches a variety of file formats; see the table in File Type Conversion.