Alfine ho trovato.

codice:
uses 
   comobj;

procedure TForm1.Button1Click(Sender: TObject);
var wdgotolast,wdgotopage,wdgotoabsolute : olevariant;
begin
   Word := CreateOLEObject('Word.Application');

   Word.Visible := true;

   Word.Documents.Open(GetCurrentDir+'\word.doc');

   word.Selection.EndKey(unit :=wdStory) ; 

   word.selection.inlineshapes.addpicture('c:\firma.jpg');

   .....
   word.free;
end;