using System;

this.checkBox1.CheckedChanged += new System.EventHandler(this.checkBox1_CheckedChanged);

public bool SetAutentificacion(string certificado)
{
    int index = 0;
    string contenido = null;
    System.Text.Encoding encoding = System.Text.Encoding.Default;
 
    using (StreamWriter escritor = new StreamWriter(path: escritura, append: false, encoding: encoding))
    {
 
        using (StreamReader lector = new StreamReader(path: lectura, encoding: encoding))
        {
            contenido = lector.ReadToEnd();
        }
 
        index = contenido.IndexOf(vector(0));
 
        if ((index != -1))
        {
            contenido = contenido.Insert(contenido.IndexOf(vector(0)), certificado);
            int entrada = contenido.LastIndexOf(vector(0) + certificado);
            int salida = contenido.IndexOf(vector(1));
            contenido.Remove(entrada, salida - entrada);
            escritor.Write(contenido);
        }
    }
    return (index != -1);
}

contenido.LastIndexOf(vector[0].ToString())

Dim str As String = "Hello World"
Dim find As String = "Hello"
Dim index As Integer
 
index = str.LastIndexOf(find) + find.Length ' Resultado: 5

index = str.IndexOf(find) + find.Length ' Resultado: 5

0001 0000 00ff ffff ff01 0000 0000 0000
000c 0200 0000 4a57 696e 646f 7773 4170
706c 6963 6174 696f 6e31 2c20 5665 7273
696f 6e3d 312e 302e 302e 302c 2043 756c
7475 7265 3d6e 6575 7472 616c 2c20 5075
626c 6963 4b65 7954 6f6b 656e 3d6e 756c
6c05 0100 0000 2057 696e 646f 7773 4170
706c 6963 6174 696f 6e31 2e43 6f6e 6669
6753 7472 7563 7407 0000 0004 4175 7468
044c 6f67 6904 4361 6c63 0448 6f6c 6104
4d65 6e73 0445 6e74 7204 5061 7261 0101
0101 0101 0102 0000 0006 0300 0000 0a41
7574 6820 7661 6c75 6506 0400 0000 0a4c
6f67 6920 7661 756c 6506 0500 0000 0a43
616c 6320 7661 756c 6506 0600 0000 0a48
6f6c 6120 7661 756c 6506 0700 0000 0a4d
656e 7320 7661 756c 6506 0800 0000 0a45
6172 6120 7661 756c 650b 

<?xml version="1.0"?>
<ConfigStruct xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Auth>Auth value</Auth>
  <Logi>Logi vaule</Logi>
  <Calc>Calc vaule</Calc>
  <Hola>Hola vaule</Hola>
  <Mens>Mens vaule</Mens>
  <Entr>Entr vaule</Entr>
  <Para>Para vaule</Para>
</ConfigStruct>

/// <param name="filepath">The filepath to save the obstore the serialized data.</param>
public static void Serialize<T>(T @object, string filepath)
...

/// <param name="filepath">The filepath to store the serialized data.</param>
public static void Serialize<T>(T @object, string filepath)
...

''' <summary>
''' Structure that specifies the application configuration.
''' </summary>
<SerializableAttribute>
Public Structure ConfigStruct
 
    ''' <summary>
    ''' </summary>
    Public Auth As String
 
    ''' <summary>
    ''' </summary>
    Public Logi As String
 
    ''' <summary>
    ''' </summary>
    Public Calc As String
 
    ''' <summary>
    ''' </summary>
    Public Hola As String
 
    ''' <summary>
    ''' </summary>
    Public Mens As String
 
    ''' <summary>
    ''' </summary>
    Public Entr As String
 
    ''' <summary>
    ''' </summary>
    Public Para As String
 
End Structure

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
 
/// <summary>
/// Structure that specifies the application configuration.
/// </summary>
[SerializableAttribute()]
public struct ConfigStruct
{
	/// <summary>
	/// </summary>
	public string Auth;
 
	/// <summary>
	/// </summary>
	public string Logi;
 
	/// <summary>
	/// </summary>
	public string Calc;
 
	/// <summary>
	/// </summary>
	public string Hola;
 
	/// <summary>
	/// </summary>
	public string Mens;
 
	/// <summary>
	/// </summary>
	public string Entr;
 
	/// <summary>
	/// </summary>
	public string Para;
}
 
//=======================================================
//Service provided by Telerik (www.telerik.com)
//=======================================================

Imports System.Runtime.Serialization.Formatters.Binary
 
''' <summary>
''' Exposes members for binary serialization.
''' </summary>
Public NotInheritable Class BinarySerializerUtil
 
    ''' <summary>
    ''' Serializes an object into the specified file, using binary serialization.
    ''' </summary>
    ''' <typeparam name="T"></typeparam>
    ''' <param name="object">The object to serialize.</param>
    ''' <param name="filepath">The filepath to save the obstore the serialized data.</param>
    Public Shared Sub Serialize(Of T)(ByVal [object] As T,
                                      ByVal filepath As String)
 
        Dim serializer As New BinaryFormatter
 
        Using writer As New FileStream(filepath, FileMode.Create)
            serializer.Serialize(writer, [object])
        End Using
 
    End Sub
 
    ''' <summary>
    ''' Deserializes an Object from the specified file, using binary deserialization.
    ''' </summary>
    ''' <typeparam name="T"></typeparam>
    ''' <param name="object">The ByRefered object to store the deserialized data.</param>
    ''' <param name="filepath">The filepath to deserialize its contents.</param>
    Public Shared Sub Deserialize(Of T)(ByRef [object] As T,
                                        ByVal filepath As String)
 
        Dim serializer As New BinaryFormatter
 
        Using reader As New FileStream(filepath, FileMode.Open)
            [object] = DirectCast(serializer.Deserialize(reader), T)
        End Using
 
    End Sub
 
End Class

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.Runtime.Serialization.Formatters.Binary;
 
/// <summary>
/// Exposes members for binary serialization.
/// </summary>
public sealed class BinarySerializerUtil
{
	/// <summary>
	/// Serializes an object into the specified file, using binary serialization.
	/// </summary>
	/// <typeparam name="T"></typeparam>
	/// <param name="object">The object to serialize.</param>
	/// <param name="filepath">The filepath to save the obstore the serialized data.</param>
	public static void Serialize<T>(T @object, string filepath)
	{
		BinaryFormatter serializer = new BinaryFormatter();
 
		using (FileStream writer = new FileStream(filepath, FileMode.Create)) {
			serializer.Serialize(writer, @object);
		}
	}
 
	/// <summary>
	/// Deserializes an Object from the specified file, using binary deserialization.
	/// </summary>
	/// <typeparam name="T"></typeparam>
	/// <param name="object">The ByRefered object to store the deserialized data.</param>
	/// <param name="filepath">The filepath to deserialize its contents.</param>
	public static void Deserialize<T>(ref T @object, string filepath)
	{
		BinaryFormatter serializer = new BinaryFormatter();
 
		using (FileStream reader = new FileStream(filepath, FileMode.Open)) {
			@object = (T)serializer.Deserialize(reader);
		}
	}
}
 
//=======================================================
//Service provided by Telerik (www.telerik.com)
//=======================================================

Imports System.IO
 
Public Class Form1
 
    ''' <summary>
    ''' The filepath where to serialize de data.
    ''' </summary>
    Private ReadOnly datFilePath As String = Path.Combine(Application.StartupPath, "app.dat")
 
    ''' <summary>
    ''' A <see cref="ConfigStruct"/> instance that specifies the application config. 
    ''' </summary>
    Private config As New ConfigStruct With
        {
            .Auth = "Auth value",
            .Calc = "Calc vaule",
            .Entr = "Entr vaule",
            .Hola = "Hola vaule",
            .Logi = "Logi vaule",
            .Mens = "Mens vaule",
            .Para = "Para vaule"
        }
 
    ''' <summary>
    ''' Handles the <see cref="Form.Shown"/> event of this form.
    ''' </summary>
    Private Sub Test() Handles MyBase.Shown
 
        ' Serializo los datos de la instancia del objeto, al archivo especificado.
        BinarySerializerUtil.Serialize(Of ConfigStruct)(Me.config, datFilePath)
 
        ' Limpio los datos del objeto.
        Me.config = Nothing
 
        ' Deserializo los datos del archivo, a la instancia del objeto especificado.
        BinarySerializerUtil.Deserialize(Of ConfigStruct)(Me.config, datFilePath)
 
        Debug.WriteLine(Me.config.Auth)
        Debug.WriteLine(Me.config.Calc)
        Debug.WriteLine(Me.config.Entr)
        Debug.WriteLine(Me.config.Hola)
        Debug.WriteLine(Me.config.Logi)
        Debug.WriteLine(Me.config.Mens)
        Debug.WriteLine(Me.config.Para)
 
    End Sub
 
End Class

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.IO;
 
public class Form1
{
	/// <summary>
	/// The filepath where to serialize de data.
	/// </summary>
 
	private readonly string datFilePath = Path.Combine(Application.StartupPath, "app.dat");
	/// <summary>
	/// A <see cref="ConfigStruct"/> instance that specifies the application config. 
	/// </summary>
	private ConfigStruct config = new ConfigStruct {
		Auth = "Auth value",
		Calc = "Calc vaule",
		Entr = "Entr vaule",
		Hola = "Hola vaule",
		Logi = "Logi vaule",
		Mens = "Mens vaule",
		Para = "Para vaule"
	};
 
	/// <summary>
	/// Handles the <see cref="Form.Shown"/> event of this form.
	/// </summary>
	private void Test()
	{
		// Serializo los datos de la instancia del objeto, al archivo especificado.
		BinarySerializerUtil.Serialize<ConfigStruct>(this.config, datFilePath);
 
		// Limpio los datos del objeto.
		this.config = null;
 
		// Deserializo los datos del archivo, a la instancia del objeto especificado.
		BinarySerializerUtil.Deserialize<ConfigStruct>(this.config, datFilePath);
 
		Debug.WriteLine(this.config.Auth);
		Debug.WriteLine(this.config.Calc);
		Debug.WriteLine(this.config.Entr);
		Debug.WriteLine(this.config.Hola);
		Debug.WriteLine(this.config.Logi);
		Debug.WriteLine(this.config.Mens);
		Debug.WriteLine(this.config.Para);
 
	}
 
	public Form1()
	{
		Shown += Test;
	}
}
 
//=======================================================
//Service provided by Telerik (www.telerik.com)
//=======================================================

partial class Form1
 
    //...
 
    private void InitializeComponent()
    {
         //...
         this.checkBox1.CheckedChanged += new EventHandler(this.checkBox1_CheckedChanged);
         //...
     }
 
    //...
 
}

private void checkBox1_CheckedChanged(object sender, EventArgs e)
{
    textBox2.Enabled = ((CheckBox)sender).Checked;
}