procedure TForm1.Button2Click(Sender: TObject);
var
OpenDialog: TOpenDialog;
begin
OpenDialog := TOpenDialog.Create(nil);
try
OpenDialog.FileName := '*.txt';
if OpenDialog.Execute then
begin
Copyfile(pchar(OpenDialog.FileName),'C:\aa.txt',false);
end;
finally
OpenDialog.Free;
end;
end;