For disabling right click on your textbox:
Put a blank contextmenuestrip on your form and rename it for ex: mycontext, then set the Contextmenuestrip property of your text box in mycontext. User will not be able right click on your textbox.
For disabling copy and paste put this code on KeyDown Event handler of your textbox
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.Modifiers == Keys.Control)
{
e.Handled = true;
textBox1.SelectionLength = 0;
}
}