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procedure TForm1.Button1Click(Sender: TObject);
var
  Source, Dest: TMemoryStream;
begin
  Source := TMemoryStream.Create;
  Source.LoadFromFile('e:\temp\temp.txt');
  Dest := TMemoryStream.Create;
  with TCompressionStream.Create(clDefault, Dest) do
  try
    CopyFrom(Source, Source.Size);
  finally
    Free;
  end;
  Dest.SaveToFile('E:\temp\dest.txt');
  Dest.Free;
  Source.Free;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  DecompressionStream: TDecompressionStream;
  Source, Dest: TMemoryStream;
begin
  Source := TMemoryStream.Create;
  Source.LoadFromFile('E:\temp\dest.txt');
  Dest := TMemoryStream.Create;
  DecompressionStream := TDecompressionStream.Create(Source);
  Dest.LoadFromStream(DecompressionStream);
  DecompressionStream.Free;
  Dest.SaveToFile('E:\temp\entpackt.txt');
  Dest.Free;
  Source.Free;
end;					

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Memo1.LoadFromStream(Dest);					

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  DecompressionStream := TDecompressionStream.Create(Source);					

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procedure ExpandStream(inStream, outStream :TStream);
const
  BufferSize = 4096;
var
  Count: Integer;
  ZStream: TDecompressionStream;
  Buffer: array[0..BufferSize-1] of Byte;
begin
  ZStream := TDecompressionStream.Create(InStream);
  try
    while True do
      begin
        Count := ZStream.Read(Buffer, BufferSize);
        if Count <> 0 then OutStream.WriteBuffer(Buffer, Count) else Break;
      end;
  finally
    ZStream.Free;
  end;
end;