function GetRarVersion(FileName: string): Double;
var
  f: file of Byte;
  Ver: Byte;
begin
  AssignFile(f, FileName);
  Reset(f);
  Seek(f, $2C);
  Read(f, Ver);
  CloseFile(f);
  Result := Ver / 10;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(FloatToStr(GetRarVersion('c:\test.rar')));
end;

uses
  ZLib;

procedure CompressStream(Source: TStream; Dest: TStream = nil; aLevel: TCompressionLevel = clFastest);
var
  DataSize: Integer;
  MemoryStream: TMemoryStream;
begin
  MemoryStream := TMemoryStream.Create;
  try
    DataSize := Source.Size;
    MemoryStream.Write(DataSize, SizeOf(DataSize));

    with TCompressionStream.Create(aLevel, MemoryStream) do
    try
      CopyFrom(Source, 0);
    finally
      Free;
    end;

    if Dest = nil then
    begin
      Source.Size := 0;
      Dest := Source;
    end;

    Dest.CopyFrom(MemoryStream, 0);
  finally
    MemoryStream.Free;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  sIn, sOut: TFileStream;
begin
  sIn := TFileStream.Create('c:\test.txt', fmOpenRead);
  try
    sOut := TFileStream.Create('c:\test.lzip', fmCreate or fmOpenWrite);
    try
      CompressStream(sIn, sOut, clMax);
    finally
      sOut.Free;
    end;
  finally
    sIn.Free;
  end;
end;

uses
  ZLib;

procedure DecompressStream(Source: TStream; Dest: TStream = nil);
var
  DataSize: Integer;
  MemoryStream: TMemoryStream;
  D: TDecompressionStream;
begin
  MemoryStream := TMemoryStream.Create;

  try
    Source.Read(DataSize, SizeOf(DataSize));
    D := TDecompressionStream.Create(Source);

    with D do
    try
      MemoryStream.CopyFrom(D, DataSize);
    finally
      D.Free;
    end;

    if Dest = nil then
    begin
      Source.Size := 0;
      Dest := Source;
    end;

    Dest.CopyFrom(MemoryStream, 0);
  finally
    MemoryStream.Free;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  sIn, sOut: TFileStream;
begin
  sIn := TFileStream.Create('c:\test.lzip', fmOpenRead);
  try
    sOut := TFileStream.Create('c:\test.txt', fmCreate or fmOpenWrite);
    try
      DecompressStream(sIn, sOut);
    finally
      sOut.Free;
    end;
  finally
    sIn.Free;
  end;
end;