我需要更改字段的内容，但是这种方式太费时间了，我该怎么办？任何人都能帮助我

procedure TForm1.Button1Click(Sender: TObject);
var
  WordApp, WordDocument, Field: OleVariant;
  I: Integer;
begin
  WordApp := CreateOleObject('Word.Application');
  try
    WordDocument := WordApp.Documents.Open('C:MyDoc.doc');
    if WordDocument.Fields.Count >= 1 then 
      for I := 1 to WordDocument.Fields.Count do
      begin
      **Field := WordDocument.Fields.Item(I);   // file size:20M，Fields.Count:30, This step takes 3 seconds**
      end;
  finally
    WordApp.Quit;
  end;
end;