Set TextBox to editable

   
  

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="WPF" Height="300" Width="300">
    <StackPanel>
        <TextBox AcceptsReturn="True" Height="100" IsReadOnly="True" 
                 Name="textBox1" TextAlignment="Left" TextWrapping="Wrap" 
                 VerticalScrollBarVisibility="Auto">
            Default starting text.
        </TextBox>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition/>
                <ColumnDefinition/>
            </Grid.ColumnDefinitions>
            <RadioButton Checked="EditableChecked" Grid.Column="0" 
                         HorizontalAlignment="Center" IsChecked="True"
                         Margin="5" Name="editableRadioButton" >
                Editable</RadioButton>
            <RadioButton Checked="EditableChecked" Grid.Column="1" 
                         HorizontalAlignment="Center" Margin="5"
                         Name="readonlyRadioButton">
                Read Only</RadioButton>
        </Grid>
    </StackPanel>
</Window>
//File:Window.xaml.cs
using System.Windows;
using System.Windows.Controls;

namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }
        private void EditableChecked(object sender, RoutedEventArgs e)
        {
            RadioButton button = e.OriginalSource as RadioButton;

            if (e.OriginalSource == editableRadioButton)
            {
                textBox1.IsReadOnly = false;
            }
            else if (e.OriginalSource == readonlyRadioButton)
            {
                textBox1.IsReadOnly = true;
            }

            textBox1.Focus();
        }
    }
}