private void GetFileFromNetUrl(string url)
        {
            try
            {
                System.Net.WebRequest req = System.Net.WebRequest.Create(url);
                req.Method = "GET";
                //獲得用戶名密碼的Base64編碼  添加Authorization到HTTP頭 不需要的賬號密碼的可以註釋下面兩行代碼
                string
 
 code = Convert.ToBase64String(Encoding.ASCII.GetBytes(string.Format("{0}:{1}", "userName", "passWord")));
                req.Headers.Add("Authorization", "Basic " + code);
                byte[] fileBytes;
                using (WebResponse webRes = req.GetResponse())
                {
                    
 
int length = (int)webRes.ContentLength;
                    HttpWebResponse response = webRes as HttpWebResponse;
                    Stream stream = response.GetResponseStream();

                    //讀取到內存
                    MemoryStream stmMemory = new MemoryStream();
                    byte[] buffer = new
 
 byte[length];
                    int i;
                    //將字節逐個放入到Byte中
                    while ((i = stream.Read(buffer, 0, buffer.Length)) > 0)
                    {
                        stmMemory.Write(buffer, 0, i);
                    }
                    fileBytes = stmMemory.ToArray();//文件流Byte，需要文件流可直接return，不需要下面的保存代碼
                    stmMemory.Close();

                    MemoryStream m = new MemoryStream(fileBytes);
                    string file = string.Format("F:\\666666666666.pdf");//可根據文件類型自定義後綴
                    FileStream fs = new FileStream(file, FileMode.OpenOrCreate);
                    m.WriteTo(fs);
                    m.Close();
                    fs.Close();
                }
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
        }    

c# 通過地址下載流然後保存文件到本地