Open a text file through a c# application

[System.Runtime.InteropServices.DllImport("shell32.dll")]
static extern void SHChangeNotify(int wEventId, int uFlags, int dwItem1, int dwItem2);
/// <summary>
/// Associate a file extension with an application
/// </summary>
/// <param name="extension">The extension to be registered (eg ".CAD")</param>
/// <param name="className">The name of the associated class (eg "CADDoc")</param>
/// <param name="description">The textual description (eg "CAD Document")</param>
/// <param name="exeProgram">The app that manages that extension (eg "c:\Cad\MyCad.exe")</param>
/// <returns></returns>
private bool CreateFileAssociation(string extension, string className, string description, string exeProgram)
    {
    const int SHCNE_ASSOCCHANGED = 0x8000000;
    const int SHCNF_IDLIST = 0;
    // Ensure that there is a leading extension indicator - full stop
    if (extension.Substring(0, 1) != ".")
        {
        extension = "." + extension;
        }
    Microsoft.Win32.RegistryKey key1 = null;
    Microsoft.Win32.RegistryKey key2 = null;
    Microsoft.Win32.RegistryKey key3 = null;
    try
        {
        // create a value for this key that contains the classname
        key1 = Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(extension);
        key1.SetValue("", className);
        // create a new key for the Class name
        key2 = Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(className);
        key2.SetValue("", description);
        // associate the program to open the files with this extension
        key3 = Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(className + @"\Shell\Open\Command");
        key3.SetValue("", exeProgram + @" ""%1""");
        }
    catch
        {
        return false;
        }
    finally
        {
        if (key2 != null)
            {
            key2.Close();
            }
        if (key3 != null)
            {
            key3.Close();
            }
        }
    // Notify Windows that file associations have changed
    SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, 0, 0);
    return true;
    }