Please see the follow codes, I hope they will help u.

CComQIPtr<MSPowerpoint::_Presentation> spActivePresentation;
//...
//...Create Active Presentation Object
//...
CString cstrFullName = spActivePresentation->FullName().GetBSTR();
CComQIPtr<MSPowerpoint::DocumentWindows> spWins;
spWins = spActivePresentation->GetWindows();
long count = spDocWins->Count;
for(int i=1; i<=count ; i++)
{
  CComQIPtr<MSPowerpoint::DocumentWindow> spEnumWin;
  spWindow = spDocWins->Item(i);
//...
//...Do some checks
//...
    HWND hWnd = (HWND)spWindow->GetHWND();
  ::SetWindowText(hWnd,cstrFullName);
}