How to convert speech (.wav file) to text file?

using System;
using System.IO;
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.Speech.Recognition;
using System.Speech.AudioFormat;
 
namespace reco
{
    public partial class Form1 : Form
    {
        private SpeechRecognitionEngine recognitionEngine;
 
        public Form1()
        {
            InitializeComponent();
            try
            {
               
                recognitionEngine = new SpeechRecognitionEngine();
                DictationGrammar dg = new DictationGrammar();
                dg.Name = "Dictation Grammar";
                recognitionEngine.LoadGrammar(dg);
                recognitionEngine.SetInputToDefaultAudioDevice();
                //recognitionEngine.SetInputToWaveFile(@"C:\Users\Deep\Music\New folder\mp3.wav");
                recognitionEngine.SetInputToDefaultAudioDevice();  // Gets sound from microphone
                recognitionEngine.EndSilenceTimeout = new TimeSpan(0, 0, 2);
                // Following two lines are not needed. They cause error!
                //recognitionEngine.Recognize();
                //recognitionEngine.RecognizeAsync();
                recognitionEngine.SpeechHypothesized += new EventHandler<SpeechHypothesizedEventArgs>(reco_SpeechHypothesized);
                recognitionEngine.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(reco_SpeechRecognized);
                recognitionEngine.RecognizeCompleted += new EventHandler<RecognizeCompletedEventArgs>(reco_RecognizeCompleted);
                recognitionEngine.AudioSignalProblemOccurred += new EventHandler<AudioSignalProblemOccurredEventArgs>(reco_AudioSignalProblemOccurred);
                recognitionEngine.SpeechDetected += new EventHandler<SpeechDetectedEventArgs>(reco_SpeechDetected);
                recognitionEngine.SpeechRecognitionRejected += new EventHandler<SpeechRecognitionRejectedEventArgs>(reco_SpeechRecognitionRejected);
                recognitionEngine.RecognizeAsync(RecognizeMode.Multiple);
            }
            catch (Exception e)
            {
                MessageBox.Show("Error "+e);
            }
        }
        private void Form1_Load(object sender, EventArgs e)
        {
 
        }
        void reco_AudioSignalProblemOccurred(object sender, AudioSignalProblemOccurredEventArgs e)
        {
            richTextBox1.AppendText(e.AudioSignalProblem.ToString());
        }
 
        void reco_SpeechHypothesized(object sender, SpeechHypothesizedEventArgs e)
        {
            richTextBox1.AppendText(e.Result.Text);
        }
 
        void reco_SpeechRecognitionRejected(object sender, SpeechRecognitionRejectedEventArgs e)
        {
            richTextBox1.AppendText("Rejected!");
        }
 
        void reco_RecognizeCompleted(object sender, RecognizeCompletedEventArgs e)
        {
            richTextBox1.AppendText("Recognition Complete!");
        }
 
        void reco_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
        {
            richTextBox1.AppendText(e.Result.Text);
        }
 
        void reco_SpeechDetected(object sender, SpeechDetectedEventArgs e)
        {
            richTextBox1.AppendText("Speech Detected!");
        }

             
        }
    }

    static void speech1(object sender, SpeechRecognizedEventArgs e)
    {
        if (e.Result.Text == "record")
        {
            showRecord();
        }
        else if (e.Result.Text == "exit")
        {
            Application.Exit();
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        showRecord();
    }
    static void showRecord()
    {
    record r=new record();
    r.show();
    }
}
public class record
{
     public  void show() { }
}