You cannot, period. Not in
RichTextBox
.
Rich text box is based on much simpler Rich Text Format, and Word is not:
https://en.wikipedia.org/wiki/Rich_Text_Format[
^].
You can learn how to parse Word (Open XML) document, map it to other document, anything, but once you use this data to show in
RichTextBox
, it won't be a Word document, not even remotely close. Note that Word is proprietary application which does not provide any libraries to be used in other applications, but let's assume that you managed to create software replicating all Word functionality, at least as a read-only software, a pure viewer, then yes, open Word, and pretty likely, RTF, but the trouble is… this software won't be
RichTextBox
, not even remotely close.
—SA