public static byte[] Compress(byte[] document)
{
    MemoryStream outStream;
    GZipStream zip;

    outStream = new MemoryStream();
    zip = new GZipStream(outStream, CompressionMode.Compress);

    zip.Write(document, 0, document.Length);
    zip.Close();

    return outStream.ToArray();
}

public static byte[] Decompress(byte[] document)
{
    MemoryStream outStream;
    GZipStream zip;
    List<byte> decompress;
    int value;

    outStream = new MemoryStream(document);
    zip = new GZipStream(outStream, CompressionMode.Decompress);

    decompress = new List<byte>();
    value = zip.ReadByte();
    while (value != -1)
    {
        decompress.Add((byte)value);

        value = zip.ReadByte();
    }

    zip.Close();

    return decompress.ToArray();
}