It's something we looked at when we first launched the File Exchange. We couldn't find anything that could read different file formats (.doc, .pdf, etc) and display a preview. It's worth looking at again though as there might be something new out now. Thanks!
I'd like to make a suggestion for improvement of file exchange. It is possible for PTO Today to purchase technology that will render a preview of many popular file types into HTML for preview. This will allow a person to see if they would like to download the file. With the growth in the number of files, this may be more important than it once used to be.