The TXT file format is simply pure text, no formatting other than perhaps tabs. What happens if you select all the text in your word document and copy and paste it into Notepad? Do you still get the weird symbols?
For reading .txt files on my DS I prefer DSReader. Using the Arial font at size 10, white text on black background, with heavy subpixel anti-aliasing, it's very readable despite the occasional repeated word. I wasn't aware Moonshell could play MP3 files while reading text, as I haven't tried the 2.0 versions, but if that's true then you may wish to look into that as a possible option as well.