If you made files in Notepad, then you are probably trying to open them on you ipaq with PocketWord.
PocketWord isn't that great of a program for reading files. You should use a dedicated reader.
And I DO NOT recommend Microsoft Reader.
Use uBook. It is free and I've opened files on it up to 12MB. It can handle more, I'm sure, but I just don't have text files that large.
Get it here: http://www.gowerpoint.com/
You want the one that says "µBook Pocket PC / 2002 / 2003 (Windows CE 3.0+) Download"
Be warned, while this is an awesome program, the navigation and default skin are a bit funky. Once you open a file, though, you're all set.