uses System.IOUtils;

procedure ConvertFileEncoding(const SourceFileName: String; const SourceEncoding: TEncoding;

  const TargetFileName: String; TargetEncoding: TEncoding);

begin

  TFile.WriteAllText(

    TargetFileName,

    TFile.ReadAllText(SourceFileName, SourceEncoding),

    TargetEncoding);

end;

procedure TForm1.Button1Click(Sender: TObject);

var

  txtANSI: TEncoding;

  Utf8: TEncoding;

begin

  txtANSI := TEncoding.GetEncoding(54936);

  Utf8 := TEncoding.UTF8;

  ConvertFileEncoding('123.txt', txtANSI, '456.txt', Utf8);

end;

procedure TForm1.Button2Click(Sender: TObject);

var

  txtANSI: TEncoding;

  Utf8: TEncoding;

  GB2312: TEncoding;

begin

  txtANSI := TEncoding.GetEncoding(65001);

  Utf8 := TEncoding.UTF8;

  GB2312 := TEncoding.ANSI;

  ConvertFileEncoding('456.txt', txtANSI, '123.txt', GB2312);

end;