Здравствуйте Odissey,
описание в .h-файле вот такое:

/* interface IM2AddOn */
/* [unique][uuid][object] */

EXTERN_C const IID IID_IM2AddOn;

MIDL_INTERFACE("C8F844A1-1878-11D0-9DF1-444553540000")
IM2AddOn : public IUnknown
{
public:
virtual HRESULT STDMETHODCALLTYPE GetAttrs(
/* [ref][out] */ TM2AddOnAttrs __RPC_FAR *AnAttrs) = 0;
virtual HRESULT STDMETHODCALLTYPE Initialize(
/* [in] */ IM2AddOnManager __RPC_FAR *AManager) = 0;
virtual HRESULT STDMETHODCALLTYPE Uninitialize( void) = 0;
virtual HRESULT STDMETHODCALLTYPE GetMacroList(
/* [out] */ IM2MacroAttrsList __RPC_FAR *__RPC_FAR *AList) = 0;
virtual HRESULT STDMETHODCALLTYPE ExecuteMacro(
/* [in] */ long ACommand,
/* [in] */ TM2String AParams) = 0;
virtual HRESULT STDMETHODCALLTYPE Notify(
/* [in] */ TM2Notify AnAdvise,
/* [in] */ IM2ParamsList __RPC_FAR *AParams) = 0;
virtual HRESULT STDMETHODCALLTYPE GetBitmap(
/* [in] */ IStream __RPC_FAR *aStm,
/* [in] */ long aBitmap) = 0;
};

#endif /* __IM2AddOn_INTERFACE_DEFINED__ */