Това работи:

Uses ComObj, ActiveX ...

...

Const

  wdWindowStateMaximize  = $00000001;

Var

  WordApp : OleVariant;

begin

  CoInitialize(Nil);

  Try

    WordApp := CreateOleObject('Word.Application');

    WordApp.Documents.Open('doc1.doc');

    WordApp.Visible := True;

    WordApp.WindowState := wdWindowStateMaximize;

  Finally

    CoUninitialize;

  End;

end;