You cannot draw on
RichTextBox
, but you can add an image through a clipboard.
Please see my past answer:
how to open word file with images and bullets in a rich text box in desktop application.[
^].
However, this is so awkward, intrusive (why modifying a Clipboard?) and weak, that I would not recommend to bother.
As to
TextBox
— just forget it. It would be much easier to make a totally custom control and add some text editing functionality to it. :-)
—SA