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

Add a SaveFileDialog, OpenFileDialog component to your form, then add "Rich Text Format|*.rtf" to Filter property of SaveFileDialog, OpenFileDialog
Step 3: Add code to handle your form
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace SaveFile
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void btnOpen_Click(object sender, EventArgs e)
{
if (openFileDialog.ShowDialog() == DialogResult.OK)
richTextBox.LoadFile(openFileDialog.FileName);
}
private void btnSave_Click(object sender, EventArgs e)
{
if (saveFileDialog.ShowDialog() == DialogResult.OK)
richTextBox.SaveFile(saveFileDialog.FileName);
}
}
}
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