Most documents at this website are stored in the universal open source format "odt". Microsoft tools such as Notepad, Word, and Wordpad are able to display raw text adequately, but are unable to display open source objects within documents such graphics, drawings, mathematical equations, and other visual objects. One fix is to read and edit an open source file in Google Docs, and that works.
A another solution is to use an open source word processor to edit documents in both open format and in proprietary format. Libreoffice is a free full word processor with versions for Macs and Windows. Get your own copy here:
https://www.libreoffice.org/download/download/ [The string 'download' appears twice.]