Printing even a plain text file is not that simple, you still need to wrap its lines, paginate it and so on, so you do need your own wxPrintOut
implementation. You can look at the printing sample included with wxWidgets to see how to do it. Or you can indeed use wxHtmlEasyPrinting
after trivial conversion of the text to HTML (basically you just need to escape the special XML entities).
Another solution is to use an external program for printing, which is the absolutely simplest way to do it, but doesn't provide any UI for the user at all.