Google Docs Viewer is very useful for displaying any doc, pdf, tiff or presentation files that are saved online.
You don't have to worry about loading your files onto any third party server and although it is a basic version, no bells and whistles, it does the job that it is meant to do very well.
You can move forwards and backwards through the document, zoom in and out and show one page or four pages at a time. You can also choose a full screen mode where you can then select to download the file.
And, of course, you can also embed the viewer. Here is a little introduction to Google Docs in the classroom!