/// <summary>
        /// 获取pdf文档的页数
        /// </summary>
        /// <param name="filePath"></param>
        /// <returns>-1表示文件不存在</returns>
        public static int GetPDFofPageCount(string filePath)
        {
            int count = -1;//-1表示文件不存在
            if (File.Exists(filePath))
            {
                using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read))
                {
                    StreamReader reader = new StreamReader(fs);
                    //从流的当前位置到末尾读取流
                    string pdfText = reader.ReadToEnd();
                    Regex rgx = new Regex(@"/Type\s*/Page[^s]");
                    MatchCollection matches = rgx.Matches(pdfText);
                    count = matches.Count;
                }
            }
            return count;
        }