I have a string of richtext characters/tokens that I would like to feed to a richtextbox in code.
string rt = @\" {\\rtf1\\ansi\\ansicpg1252\\deff0\\deflang
Rich textbox has a property named Rtf. Set that property to your string value. Also, your string has an extra space as the first character. I had to remove that before I saw your Hello World.
Expanding on gbogumil's answer:
string rt = @"{\rtf1\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{\f0\fswiss\fcharset0 Arial;}{\f1\fnil\fprq2\fcharset0 Biondi;}}"+
@"{\colortbl ;\red255\green0\blue0;}"+
@"{\*\generator Msftedit 5.41.15.1507;}\viewkind4\uc1\pard\f0\fs20\par"+
@"\cf1\f1 hello\cf0\f0 \ul world\par}";
this.richTextBox1.Rtf = rt;