uses Printers;
 
procedure TForm1.Button1Click(Sender: TObject);
var
Device : array[0..255] of char;
Driver : array[0..255] of char;
Port   : array[0..255] of char;
hDMode : THandle;
PDMode : PDEVMODE;
Printer: TPrinter;
begin
  Printer:=TPrinter.Create;
  Printer.PrinterIndex := Printer.PrinterIndex;
  Printer.GetPrinter(Device, Driver, Port, hDMode);
  if hDMode <> 0 then begin
    pDMode := GlobalLock(hDMode);
    if pDMode <> nil then begin
 
     {Set to legal}
      pDMode^.dmFields := pDMode^.dmFields or dm_PaperSize;
      pDMode^.dmPaperSize := DMPAPER_LEGAL;
 
     {Set to custom size}
      pDMode^.dmFields := pDMode^.dmFields or
                          DM_PAPERSIZE or
                          DM_PAPERWIDTH or
                          DM_PAPERLENGTH;
      pDMode^.dmPaperSize := DMPAPER_USER;
      pDMode^.dmPaperWidth := 100 {SomeValueInTenthsOfAMillimeter};
      pDMode^.dmPaperLength := 100 {SomeValueInTenthsOfAMillimeter};
 
     {Set the bin to use}
      pDMode^.dmFields := pDMode^.dmFields or DMBIN_MANUAL;
      pDMode^.dmDefaultSource := DMBIN_MANUAL;
 
      GlobalUnlock(hDMode);
    end;
  end;
  Printer.PrinterIndex := Printer.PrinterIndex;
  Printer.BeginDoc;
  Printer.Canvas.TextOut(100,100, 'Test 1');
  Printer.EndDoc;
end;