uses
 WinSpool;
{ Function SetPrinterToPort
 Parameters :
  hPrinter: handle of printer to change, obtained from OpenPrinter
  port: port name to use, e.g. LPT1:, COM1:, FILE:
 Returns:
  The name of the previous port the printer was attached to.
 Description:
  Changes the port a printer is attached to using Win32 API functions.
        The changes made are NOT local to this process, they will affect all
        other processes that try to use this printer! It is recommended to set the
        port back to the old port returned by this function after
        the end of the print job.
 Error Conditions:
  Will raise EWin32Error exceptions if SetPrinter or GetPrinter fail.
 Created:
  21.10.99 by P. Below}
function SetPrinterToPort(hPrinter: THandle; const port: string): string;
var
 pInfo: PPrinterInfo2;
 bytesNeeded: DWORD;
begin
 {Figure out how much memory we need for the data buffer. Note that GetPrinter is
 supposed to fail with a specific error code here. The amount of memory will
    be larger than Sizeof(TPrinterInfo2) since variable amounts of data are appended
    to the record}
 SetLastError(NO_ERROR);
 GetPrinter(hPrinter, 2, nil, 0, @bytesNeeded);
 if GetLastError <> ERROR_INSUFFICIENT_BUFFER then
  RaiseLastWin32Error;
 pInfo := AllocMem(bytesNeeded);
 try
  if not GetPrinter(hPrinter, 2, pInfo, bytesNeeded, @bytesNeeded) then
  RaiseLastWin32Error;
  with pInfo^ do
  begin
  Result := pPortname;
  pPortname := @port[1];
  end;
  if not SetPrinter(hPrinter, 2, pInfo, 0) then
  RaiseLastWin32Error;
 finally
  FreeMem(pInfo);
 end;
end;
function GetCurrentPrinterHandle: THandle;
var
 Device, Driver, Port: array[0..255] of char;
 hDeviceMode: THandle;
begin
 Printer.GetPrinter(Device, Driver, Port, hDeviceMode);
 if not OpenPrinter(@Device, Result, nil) then
  RaiseLastWin32Error;
end;

uses Printers;

{$IFNDEF WIN32}

const MAX_PATH = 144;

{$ENDIF}

procedure TForm1.Button1Click(Sender: TObject);

var

 pDevice: pChar;

 pDriver: pChar;

 pPort: pChar;

 hDMode: THandle;

 PDMode: PDEVMODE;

begin

 if PrintDialog1.Execute then

 begin

  GetMem(pDevice, cchDeviceName);

  GetMem(pDriver, MAX_PATH);

  GetMem(pPort, MAX_PATH);

  Printer.GetPrinter(pDevice, pDriver, pPort, hDMode);

  Printer.SetPrinter(pDevice, PDriver, 'FILE:', hDMode);

  FreeMem(pDevice, cchDeviceName);

  FreeMem(pDriver, MAX_PATH);

  FreeMem(pPort, MAX_PATH);

  Printer.BeginDoc;

  Printer.Canvas.TextOut(100, 100, 'Delphi World Is Wonderful!');

  Printer.EndDoc;

 end;

end;