Not sure if you have some specific criteria for this or not, but here is a small sample that puts text into the RTF control, selects some text, copies it, then pastes it somewhere else in the RTF control. This utilizes the "Copy" method (which will copy it to the clipboard), but there are other ways to do it if you don't want to put it on the clipboard.
Code Snippet
private void Form1_Load(object sender, EventArgs e)
{
rtb.Text = "This is some text to practice cut/copy/paste operations.";
}
private void button1_Click(object sender, EventArgs e)
{
rtb.Select(10, 20);
rtb.Copy();
rtb.SelectionStart = 50;
rtb.SelectionLength = 0;
rtb.Paste();
}
(FYI - There is also a "Cut" method on the RTF control.)