Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

{ 
  This code displays the application/file "Open With" dialog 
  Passing the full file path and name as a parameter will cause the 
  dialog to display the line "Click the program you want to use to open 
  the file 'filename'". 
}

 uses
   ShellApi;

   procedure OpenWith(FileName: string);
 begin
   ShellExecute(Application.Handle, 'open', PChar('rundll32.exe'),
     PChar('shell32.dll,OpenAs_RunDLL ' + FileName), nil, SW_SHOWNORMAL);
 end;


 procedure TForm1.Button1Click(Sender: TObject);
 begin
   if Opendialog1.Execute then
     OpenWith(Opendialog1.FileName);
 end;