All of the Notepad "hidden text" tricks can be sumemd into one easter egg:

1> Open Notepad
2> Enter four words separated by spaces, wherein the first word has 4 letters, the next two have three letters, and the last word has five letters
3> DON'T hit enter at the end of the line.
4> Save the file.
5> Close Notepad.
6> Reopen Notepad.
7> Open the file you just saved.

It will now have the "hidden text" in place of your original text.

This seems to work for any legitimate words, and also for a few random letters I tested.

It also seems to work with certain number combos, such as "4444 333 333 55555" and such.

Note: do NOT "save as" anything. Only "save" the file, and also, don't replace an existing file or it won't work either.