如何打开我的CHM文件?

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls,shellapi;type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    hh: HINST;
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.DFM}procedure TForm1.Button1Click(Sender: TObject);
begin
  if hh = 0 then
    hh := ShellExecute(application.Handle,'open','C:\netants\NetAnts.chm',nil,nil,SW_SHOW);
end;procedure TForm1.FormCreate(Sender: TObject);
begin
  hh := 0;
end;procedure TForm1.FormDestroy(Sender: TObject);
begin
  sendmessage(FindWindow(nil,'网络蚂蚁使用手册'),wm_close,0,0);
end;end.