For non-image files, it is highly recommended that one present the file in adobe PDF format. It would only be necessary to present a file in an “office” or editable format, such as word or excel, if you wanted people to be able to take that document and continue to edit it.
A PDF is more universally accessible (not everyone has MsOffice on their PC, but the adobe reader is freely available), and is usually quicker to load for the reader. There are also some fast loading readers out there.
PDF conveys a more professional impression of your web. If you do not have a PDF writer on your system there are a number of possibilities to convert the existing file. http://www.pdfonline.com/ allow you to convert a number of formats to the PDF format online.
Alternatively you could install a PDF writer. If you are on a tight budget, there are a number of serviceable PDF writers available for free. These work on Vista as well as earlier versions of windows.