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procedure TForm1.btnUnZIPClick(Sender: TObject);
var ZIPStream: TDecompressionStream;
    SrcStream: TMemoryStream;
    Buffer: string[200];
    s: string;

    size : integer;
begin
  SrcStream := TMemoryStream.Create;
  SrcStream.LoadFromFile(ExtractFilePath(Application.Exename)+'Test.file');
  ZIPStream := TDecompressionStream.Create(SrcStream);

  Size := SrcStream.Size;

  ZIPStream.Seek(0,soFromBeginning);

  s := '';
  while ZIPStream.Position < ZIPStream.Size do begin
    Buffer := '';
    ZIPStream.ReadBuffer(Buffer,200);
    s := s+Buffer;
    dec(size,200);
    ZipStream.Seek(0,soFromCurrent);
  end;

  ZIPStream.Free;
  SrcStream.Free;
  Memo1.Text := s;
end;