Set The Title Of A File, Which You Opened From The Dialogbox

It Will Open File Dialog Box & Then It Will Open Selected Text File Or RTF File Into The Richtextbox.

private void button4_Click(object sender, EventArgs e) { string filename = null; if (OpenFileDialog1.ShowDialog == DialogResult.OK) { //Store Selected File Name In the Variable... filename = OpenFileDialog1.FileName; //Load Selected File Into The RichtextBox... RichTextBox1.LoadFile(filename); }   //Set The Form Title Name As Filename..... this.Text = filename; }