//-------------------------------------------------------------------------
//  function to return the type of executable or dll (DOS, 16-bit, 32-bit).  
//  Thanks to Peter Below (TeamB) for this code. 
//-------------------------------------------------------------------------

type
  TExeType = (etUnknown, etDOS, etWinNE {16-bit}, etWinPE {32-bit});

function GetExeType(const FileName: string): TExeType;
var
  Signature,
  WinHdrOffset: Word;
  fexe: TFileStream;
begin
  Result := etUnknown;
  try
    fexe := TFileStream.Create(FileName, fmOpenRead or fmShareDenyNone);
    try
      fexe.ReadBuffer(Signature, SizeOf(Signature));
      if Signature = $5A4D { 'MZ' } then
        begin
          Result := etDOS;
          fexe.Seek($18, soFromBeginning);
          fexe.ReadBuffer(WinHdrOffset, SizeOf(WinHdrOffset));
          if WinHdrOffset >= $40 then
            begin
              fexe.Seek($3C, soFromBeginning);
              fexe.ReadBuffer(WinHdrOffset, SizeOf(WinHdrOffset));
              fexe.Seek(WinHdrOffset, soFrombeginning);
              fexe.ReadBuffer(Signature, SizeOf(Signature));
              if Signature = $454E { 'NE' } then
                Result := etWinNE
              else
                if Signature = $4550 { 'PE' } then
                  Result := etWinPE;
            end;
        end;
    finally
      fexe.Free;
    end;
  except
  end;
end;

begin
  case GetExeType(aFileName) of
    etUnknown: Label3.Caption := 'Unknown file type';
    etDOS : Label3.Caption := 'DOS executable';
    etWinNE : {16-bit} Label3.Caption := 'Windows 16-bit executable';
    etWinPE : {32-bit} Label3.Caption := 'Windows 32-bit executable';
  end;
end;