For this file I just opened it in Wordpad (drag and drop onto a desktop shortcut). It is not a straight text file, but you can read/copy the text portions.
You can do this with any unknown file. Many small files with unknown extensions are simply text files (config.div, etc); if there is a mix of binary and text data, you will be able to see the text and if it is binary data there is no harm done (for that you would need either a program that recognizes the format or a hex editor).
If a file is primarily binary data, but contains some text (such as the data.000 file in the save folders), there are programs available to extract just the text portions (this can give to an idea of the structure of the file).
I have not looked at any other game files (outside the save folders) besides the sound and books files.
