Use KeyBinding to bind Key event to TextBox.InputBindings

   
  
<Window x:Class="Commands.NoCommandTextBox"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="NoCommandTextBox" Height="300" Width="300">
    <Grid>
      <TextBox Name="txt"/>
    </Grid>
</Window>
//File:Window.xaml.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace Commands
{
    public partial class NoCommandTextBox : System.Windows.Window
    {
        public NoCommandTextBox()
        {
            InitializeComponent();           
        
            txt.InputBindings.Add(new KeyBinding(ApplicationCommands.NotACommand, Key.C, ModifierKeys.Control));
        }
     
        private void SuppressCommand(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = false;
            e.Handled = true;
        }
    }
}