Making a text file for the Pleco 2 reader is pretty simple on Windows. (Please add instructions for a MAC and for Linux)
The simplest way is to use the built in Notepad application.
You can directly enter the text using an IME, or paste the text from another source, such as a PDF. When you save the notepad file, you must change the encoding to Unicode. This is at the bottom of the “Save As” dialog window.