uses
 Printers, Winspool;
function SpoolFile(const FileName, PrinterName: string): Integer;
var
 Buffer: record
  JobInfo: record // ADDJOB_INFO_1
  Path: PChar;
  JobID: DWORD;
  end;
  PathBuffer: array[0..255] of Char;
 end;
 SizeNeeded: DWORD;
 Handle: THandle;
 PrtName: string;
 ok: Boolean;
begin
 // Flush job to printer
 PrtName := PrinterName;
 if PrtName = '' then
  PrtName := Printer.Printers[Printer.PrinterIndex]; // Default printer name
 ok := False;
 if OpenPrinter(PChar(PrtName), Handle, nil) then
  if AddJob(Handle, 1, @Buffer, SizeOf(Buffer), SizeNeeded) then
  if CopyFile(PChar(FileName), Buffer.JobInfo.Path, True) then
  if ScheduleJob(Handle, Buffer.JobInfo.JobID) then
  ok := True;
 if not ok then Result := GetLastError
 else
  Result := 0;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
 if SpoolFile('c:\test.prn', Printer.Printers[0]) = 0 then
  ShowMessage('No error...');
end;