text selection and highlighting with the mouse could be tricky but the rest is easy to do with draw_text() and your own input functions. it wouldn't work better in c++ either.

you can't use mfc controls in a directx window.

maybe you could use some external directx gui system like cegui or something. i think there also are some directx gui widgets included in the directx sdk but i don't know if there is anything useful for text editing.