documents are in PDF format (Portable Document
Format). There are many non-proprietary PDF readers available
- pdfreaders.org has a list.
Acrobat Reader is free software that allows you to view, print, search and distribute PDF documents.
You can get the latest free version from www.adobe.com
LibreOffice.org is a free to download office suite. A plugin for MS Office is available which allows the reading of the Libreoffice.org spreadsheets (- the .ods files and other OpenDocument formats) - it can be downloaded here LibreOffice.org can open MS Office documents out-of-the-box!
And now the historical stuff..