Not all mobile browsers posses native support for PDF, DOC and other formats. But, by leveraging Google's Document Viewer, you're able to present these files to mobile users. For example:
http://docs.google.com/viewer?url=www.mysite.com/brochure.pdf
Note the lack of the "http://" protocol specifier in the URL. For some reason, if you include this, Google's Viewer will report back a permissions issue and fail to show the document.