Step 1: Click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "ReadRtfFile" and then click OK
Step 2: Design your form as below

Step 3: Add code to button click event handler as below
//Open file dialog, allows you to select a rtf file
private void btnOpen_Click(object sender, EventArgs e)
{
using (OpenFileDialog ofd = new OpenFileDialog() { Filter = "Rich Text Format|*.rtf", ValidateNames = true, Multiselect = false })
{
if (ofd.ShowDialog() == DialogResult.OK)
richTextBox.LoadFile(ofd.FileName);
}
}
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