Just upload the file using the DW File Panel and link to it in your web page as you would any other file.
If you want to force a download then zip the file and link to the zipped file.
upload the file you want people to download to your webserver, add a link to the file in your web page, upload the web page to your webserver.
Zip the file. In most cases zipped files will force a download instead of opening the file in Acrobat Reader.
If you want 100% reliability, do a Google Search for Force Download Script in the programming language supported by your web server (PHP, ASP, CF..)