Копирование большого файла в буфер обмена

function _hread(FileHandle: word; BufPtr: pointer;
  ByteCount: longint): longint; far;
  external 'KERNEL' index 349;

procedure CopyFileToClipboard(const fname: string);
var
  hmem, hFile: THandle;
  size: LongInt;
  p: Pointer;
begin
  hFile := FileOpen(fname, fmOpenRead);
  try
    size := FileSeek(hFile, 0, 2);
    FileSeek(hfile, 0, 0);
    if size > 0 then
    begin
      hmem := GlobalAlloc(GHND, size);
      if hMem <> 0 then
      begin
        p := GlobalLock(hMem);
        if p <> nil then
        begin
          _hread(hFile, p, size);
          GlobalUnlock(hMem);
          Clipboard.SetAsHandle(CF_TEXT, hMem);
        end
        else
          GlobalFree(hMem);
      end;
    end;
  finally
    FileClose(hFile);
  end;
end;

procedure TForm1.SpeedButton2Click(Sender: TObject);
var
  fname: string[128];
begin
  if OpenDialog1.Execute then
  begin
    fname := OpenDialog1.Filename;
    CopyFileToClipboard(fname);
  end;
end;