uses 
  Registry; 

function IsWordInstalled: Boolean; 
var 
  Reg: TRegistry; 
  s: string; 
begin 
  Reg := TRegistry.Create; 
  try 
    Reg.RootKey := HKEY_CLASSES_ROOT; 
    Result := Reg.KeyExists('Word.Application'); 
  finally 
    Free; 
  end; 
end; 

procedure TForm1.Button1Click(Sender: TObject); 
begin 
  if IsWordInstalled then 
    ShowMessage('MS Word is installed.'); 
end;