what is the meaning of the forth parameter of the method Presentations::open?

I create ppt  by the following method,it run ok.

PowerPoint::PresentationsPtr _apps = lpParent;
_apps->Open(bstrFileName,msoFalse,NULL,msoTrue);

if the forth parameter 'WithWindow'=msoFalse, it runs error.what's it meaning?

by the way,if i create ppt by the following method,how do I set the property like this parameter.

SCODE sc = ::OleCreateFromFile(clsid, T2COLE(lpszFileName),
        IID_IUnknown, render, lpFormatEtc, m_lpClientSite, m_lpStorage,
        (LPLP)&m_lpObject);