/// <summary>
    /// Definition for interface IPersist.
    /// </summary>
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("0000010c-0000-0000-C000-000000000046")]
    public interface IPersist {
        /// <summary>
        /// getClassID
        /// </summary>
        /// <param name="pClassID"></param>
        void GetClassID( /* [out] */ out Guid pClassID);
    };
    /// <summary>
    /// Definition for interface IPersistStream.
    /// </summary>
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("00000109-0000-0000-C000-000000000046")]
    public interface IPersistStream : IPersist {
        /// <summary>
        /// GetClassID
        /// </summary>
        /// <param name="pClassID"></param>
        new void GetClassID(out Guid pClassID);
        /// <summary>
        /// isDirty
        /// </summary>
        /// <returns></returns>
        [PreserveSig]
        int IsDirty( );
        /// <summary>
        /// Load
        /// </summary>
        /// <param name="pStm"></param>
        void Load([In] IStream pStm);
        /// <summary>
        /// Save
        /// </summary>
        /// <param name="pStm"></param>
        /// <param name="fClearDirty"></param>
        void Save([In] IStream pStm, [In, MarshalAs(UnmanagedType.Bool)] bool fClearDirty);
        /// <summary>
        /// GetSizeMax
        /// </summary>
        /// <param name="pcbSize"></param>
        void GetSizeMax(out long pcbSize);
    };

     // Example -----------------------------------------------------------------------------------------
       public  string    _strErrorMsg;

       public string GetComObjectGUID(object objComCtrl)
    {
        IStream comStream;
        IntPtr pIPStream = IntPtr.Zero;
        string strStreamGUID = "NONE";
        IntPtr hGlobalMemHandle = (IntPtr)null;
        IntPtr pActiveXObj = IntPtr.Zero;
        bool bRetc = true;
        int iResult;
        int S_OK = 0;
        int E_FAIL = unchecked((int)0x80004005);
        int E_NOINTERFACE = unchecked((int)0x80004002);
        Guid IID_IPersistStreamInit = new Guid("7FD52380-4E07-101B-AE2D-08002B2EC713");

        if (Marshal.IsComObject((object)objComCtrl))
        {
        pActiveXObj = Marshal.GetIUnknownForObject((object)objComCtrl);
        if (pActiveXObj == IntPtr.Zero)
        {
            ErrorMsg = "GetIUnknownForObject was zero.";
        }
        else
        {
            iResult = Marshal.QueryInterface(pActiveXObj, ref IID_IPersistStreamInit, out pIPStream);
            if (iResult == E_NOINTERFACE)
            {
            ErrorMsg = "No such interface supported";
            }
            else if (iResult == E_FAIL)
            {
            ErrorMsg = "PersistStreamInit QueryInit failed.";
            }
            else if (iResult == S_OK)
            {
            IPersistStreamInit pPersistStream = (IPersistStreamInit)Marshal.GetObjectForIUnknown(pIPStream);
            Guid ptrClsId = new Guid();
            pPersistStream.GetClassID(ref ptrClsId);
            strStreamGUID = ptrClsId.ToString().ToUpper();
            }
        }
        }
        return (strStreamGUID);
    }

    public string ErrorMsg
     {
          get {return _strErrorMsg;}
          set {_strErrorMsg = value;}
     }