Machen Sie den text Fett wechseln nach Tastendruck

Ich habe ein Formular, in C#, dass einige Tasten. Ich möchte, dass wenn der button gedrückt wird, machen den text Fett.

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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;
using System.Net;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //string str = @"C:\windows\system32\notepad.exe";
            //string str = @"C:\windows\system32\winamp.exe";
            string str = @"C:\priority\bin.95\WINMENU.exe";
            Process process = new Process();
            process.StartInfo.FileName = str;
            process.Start(); 
        }

        private void button2_Click(object sender, EventArgs e)
        {
            //string str = @"C:\windows\system32\notepad.exe";
            //string str = @"C:\windows\system32\winamp.exe";
            string str = @"C:\Program Files\UltraVNC\vncviewer.exe";
            Process process = new Process();
            process.StartInfo.FileName = str;
            process.Start(); 
        }

        private void button3_Click(object sender, EventArgs e)
        {
        }

        private void button3_Click_1(object sender, EventArgs e)
        {
            //string str = @"C:\windows\system32\notepad.exe";
            //string str = @"C:\windows\system32\winamp.exe";
            string str = @"C:\Program Files\UltraVNC\vncviewer.exe";
            Process process = new Process();
            process.StartInfo.FileName = str;
            process.Start(); 
        }

        private void button4_Click(object sender, EventArgs e)
        {
            //string str = @"C:\windows\system32\notepad.exe";
            //string str = @"C:\windows\system32\winamp.exe";
            string str = @"C:\Windows\system32\mstsc.exe";
            Process process = new Process();
            process.StartInfo.FileName = str;
            process.Start();
        }

        private void button5_Click(object sender, EventArgs e)
        {
           //string str = @"C:\windows\system32\notepad.exe";
            //string str = @"C:\windows\system32\winamp.exe";
            string str = @"C:\Program Files\Microsoft Office\Office14\winword.exe";
            Process process = new Process();
            process.StartInfo.FileName = str;
            process.Start();

        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {


        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void pictureBox1_Click(object sender, EventArgs e)
        {

        }
    }
}

was soll ich jetzt tun ?