压缩方法
public void compressFile(string M_str_DFile, string M_str_CFile)
        {
            if (!File.Exists(M_str_DFile)) throw new FileNotFoundException();
            using (FileStream sourceStream = new FileStream(M_str_DFile, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite))
            {
                byte[] buffer = new byte[sourceStream.Length];
                int checkCounter = sourceStream.Read(buffer, 0, buffer.Length);
                if (checkCounter != buffer.Length) throw new ApplicationException();
                using (FileStream destinationStream = new FileStream(M_str_CFile, FileMode.OpenOrCreate, FileAccess.Write))
                {
                    using (GZipStream compressedStream = new GZipStream(destinationStream, CompressionMode.Compress, true))
                    {
                        compressedStream.Write(buffer, 0, buffer.Length);
                    }
                }
            }
        }

button 事件
 private void btnFCut_Click(object sender, EventArgs e)
        {
            try
            {
                doperate.compressFile(txtFile.Text.Trim(), txtDCPath.Text.Trim() + ".rar");
                MessageBox.Show("文件压缩成功！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            btnDCut.Enabled = true;
            txtDCPath.ReadOnly = true;
            btnFCut.Enabled = false;
        }

问题:
    为什么单击文件压缩按纽后压缩的压缩文件 再解压缩后还原的文件不可识别(例如把.txt文件压缩后再解压缩系统不显示是.txt文件)　麻烦明日的软件工程师们帮我解决一下　，谢谢！
顺便问一下　在项目里引用sharpziplib.dll也能压缩　压缩解压怎么写　怎么引用sharpziplib.dll　我怎么在项目里找不到sharpziplib.dll