请问如何在程序里把word文档、网页文件等格式转换为纯文本格式？

Question

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, OleServer, ComObj, Word2000;type
  TForm1 = class(TForm)
    Button1: TButton;
    WordApplication1: TWordApplication;
    procedure Button1Click(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    wordaaa:Variant;
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
begin
    try
    wordaaa:=CreateOLEObject('word.application');
    except
    Application.MessageBox('无法打开该文件，请确认已经安装WORD.','',MB_OK+MB_IconStop);
    Exit;
    end;
    wordaaa.visible:=false;
    wordaaa.documents.open('d:\test.rtf');
    wordaaa.ActiveDocument.saveas('d:\change.tmp',wdFormatText);
end;procedure TForm1.FormDestroy(Sender: TObject);
begin
    wordaaa.Activedocument.close;
end;end.