Question

After getting the text in the RichTextBox I want to clear the text. How can I do that?

TextRange txt = new TextRange(richtxtSNotice.Document.ContentStart, richtxtSNotice.Document.ContentEnd);
MessageBox.Show(txt.Text);

Answer 1

Try to create a TextRange with RichBoxText content, then set Text to empty string:

TextRange txt = new TextRange(richtxtSNotice.Document.ContentStart, richtxtSNotice.Document.ContentEnd);
txt.Text = "";