/// <summary>
/// Create an associaten for a file extension in the windows registry
/// CreateAssociation(@"vendor.application",".tmf","Tool file",@"C:\Windows\SYSWOW64\notepad.exe",@"%SystemRoot%\SYSWOW64\notepad.exe,0");
/// </summary>
/// <param name="ProgID">e.g. vendor.application</param>
/// <param name="extension">e.g. .tmf</param>
/// <param name="description">e.g. Tool file</param>
/// <param name="application">e.g.  @"C:\Windows\SYSWOW64\notepad.exe"</param>
/// <param name="icon">@"%SystemRoot%\SYSWOW64\notepad.exe,0"</param>
/// <param name="hive">e.g. The user-specific settings have priority over the computer settings. KeyHive.LocalMachine  need admin rights</param>
public static void CreateAssociation(string ProgID, string extension, string description, string application, string icon, KeyHiveSmall hive = KeyHiveSmall.CurrentUser)
{
    RegistryKey selectedKey = null;

    switch (hive)
    {
        case KeyHiveSmall.ClassesRoot:
            Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(extension).SetValue("", ProgID);
            selectedKey = Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(ProgID);
            break;

        case KeyHiveSmall.CurrentUser:
            Microsoft.Win32.Registry.CurrentUser.CreateSubKey(@"Software\Classes\" + extension).SetValue("", ProgID);
            selectedKey = Microsoft.Win32.Registry.CurrentUser.CreateSubKey(@"Software\Classes\" + ProgID);
            break;

        case KeyHiveSmall.LocalMachine:
            Microsoft.Win32.Registry.LocalMachine.CreateSubKey(@"Software\Classes\" + extension).SetValue("", ProgID);
            selectedKey = Microsoft.Win32.Registry.LocalMachine.CreateSubKey(@"Software\Classes\" + ProgID);
            break;
    }

    if (selectedKey != null)
    {
        if (description != null)
        {
            selectedKey.SetValue("", description);
        }
        if (icon != null)
        {
            selectedKey.CreateSubKey("DefaultIcon").SetValue("", icon, RegistryValueKind.ExpandString);
            selectedKey.CreateSubKey(@"Shell\Open").SetValue("icon", icon, RegistryValueKind.ExpandString);
        }
        if (application != null)
        {
            selectedKey.CreateSubKey(@"Shell\Open\command").SetValue("", "\"" + application + "\"" + " \"%1\"", RegistryValueKind.ExpandString);
        }
    }
    selectedKey.Flush();
    selectedKey.Close();
}
/// <summary>
/// Creates a association for current running executable
/// </summary>
/// <param name="extension">e.g. .tmf</param>
/// <param name="hive">e.g. KeyHive.LocalMachine need admin rights</param>
/// <param name="description">e.g. Tool file. Displayed in explorer</param>
public static void SelfCreateAssociation(string extension, KeyHiveSmall hive = KeyHiveSmall.CurrentUser, string description = "")
{
    string ProgID = System.Reflection.Assembly.GetExecutingAssembly().EntryPoint.DeclaringType.FullName;
    string FileLocation = System.Reflection.Assembly.GetExecutingAssembly().Location;
    CreateAssociation(ProgID, extension, description, FileLocation, FileLocation + ",0", hive);
}