Example: Index.of Private Jpg -ac -gov How Do I Specify Google To Search Say For Example Pdf Documents And Other Specified Fily Types?

How do i specify google to search say for example pdf documents and other specified fily types? - example: index.of private jpg -ac -gov

PDF, if you look only at Google, what shall I write, and how can I do to reasults index shows page. And what about the apache index page? and if I wanted to look for files Texy What should I write?