How can I get a string that contains RTF format codes into a RichTextBox

Use the Rtf property of the control.

	richTextBox1.Rtf = @'{\rtf1\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{\f0\fswiss\fcharset0 Arial;}}\viewkind4\uc1\pard\b\i\f0\fs20 This is bold italics.\par }';