Автор: http://www.swissdelphicenter.ch

uses
  Printers, WinSpool;

procedure GetPapernames(sl: TStrings);
type
  TPaperName = array[0..63] of Char;
  TPaperNameArray = array[1..High(Word) div SizeOf(TPaperName)] of TPaperName;
  PPapernameArray = ^TPaperNameArray;
var
  Device, Driver, Port: array[0..255] of Char;
  hDevMode: THandle;
  i, numPaperformats: Integer;
  pPaperFormats: PPapernameArray;
begin
  Printer.PrinterIndex := -1; // Standard printer
  Printer.GetPrinter(Device, Driver, Port, hDevmode);
  numPaperformats := WinSpool.DeviceCapabilities(Device, Port, DC_PAPERNAMES,
    nil, nil);
  if numPaperformats 0 then
  begin
    GetMem(pPaperformats, numPaperformats * SizeOf(TPapername));
    try
      WinSpool.DeviceCapabilities(Device, Port, DC_PAPERNAMES,
        PChar(pPaperFormats), nil);
      sl.Clear;
      for i := 1 to numPaperformats do
        sl.Add(pPaperformats^[i]);
    finally
      FreeMem(pPaperformats);
    end;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  GetPapernames(memo1.Lines);
end;