Somehow, I didn't see the attached document of post 5 until now, actually I didn't see the post at all funnily, only the RTF codes of post 6, so that was what I replied to post 7.
I have now examined the uploaded .rtf document, here the header does not display in the RichTextBox, which suggests the format is incompatible. I can open it in WordPad to see the header there, also OpenOffice Writer displays the header fine. From WordPad I saved the file as a copy with its 'rich text format', the file size is now decreased from 67kb to 9kb, I have attached this file here and it displays the header when loaded into RichTextBox now. The original file must be coded by a newer RTF standard that can't be read with current rtf engine in .Net Framework.