To view downloaded documents from this and other websites you will need to have a couple of common, free software viewers installed on your computer. It's also a good idea to occasionally download new versions.

Adobe Acrobat Reader is used to view PDF-format files.
http://www.adobe.com

Djvu viewer is used to view DJVU-format files.
http://www.celartem.com

Google Earth is used to view KML map files.
http://earth.google.com

Once installed, documents you click on and download should open correctly. If they are not installed, your computer will ask a question like “What program should I use to open this file?”

The above links provide both the software and instructions on how to install them.