[DllImport("advapi32.dll", SetLastError = true)]
        private static extern bool LogonUser(string
        lpszUsername, string lpszDomain, string lpszPassword,
        int dwLogonType, int dwLogonProvider, ref IntPtr phToken);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool CloseHandle(IntPtr handle);

        [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public extern static bool DuplicateToken(IntPtr existingTokenHandle,
        int SECURITY_IMPERSONATION_LEVEL, ref IntPtr duplicateTokenHandle);


        // logon types
        const int LOGON32_LOGON_INTERACTIVE = 2;
        const int LOGON32_LOGON_NETWORK = 3;
        const int LOGON32_LOGON_NEW_CREDENTIALS = 9;

        // logon providers
        const int LOGON32_PROVIDER_DEFAULT = 0;
        const int LOGON32_PROVIDER_WINNT50 = 3;
        const int LOGON32_PROVIDER_WINNT40 = 2;
        const int LOGON32_PROVIDER_WINNT35 = 1;

        static string HelpUserName = System.Configuration.ConfigurationManager.AppSettings["HelpUserName"];
        static string HelpDomain = System.Configuration.ConfigurationManager.AppSettings["HelpDomain"];
        static string HelpPassword = System.Configuration.ConfigurationManager.AppSettings["HelpPassword"];
        static string HelpFilePath = System.Configuration.ConfigurationManager.AppSettings["HelpFilePath"];

public static byte[] GetFile(string DownFileName)
        {
            byte[] DownloadFile = null;//要下载的文件的数据

            IntPtr tokenHandle = new IntPtr(0);
            IntPtr dupeTokenHandle = new IntPtr(0);
            tokenHandle = IntPtr.Zero;
            bool returnValue = LogonUser(HelpUserName, HelpDomain, HelpPassword, LOGON32_LOGON_NEW_CREDENTIALS, LOGON32_PROVIDER_DEFAULT, ref tokenHandle);
            if (returnValue == false)
            {
                int ret = Marshal.GetLastWin32Error();
                throw new System.ComponentModel.Win32Exception(ret);
            }
            WindowsIdentity newId = null;
            WindowsImpersonationContext impersonatedUser = null;
            using (newId = new WindowsIdentity(tokenHandle))
            {
                using (impersonatedUser = newId.Impersonate())
                {//操作文档
                    string filePath = HelpFilePath + "\\" + DownFileName;//图片存放路径
                    DownloadFile = File.ReadAllBytes(filePath);//获取文件数据
                }
            }
            impersonatedUser.Undo();
            if (tokenHandle != IntPtr.Zero)
                CloseHandle(tokenHandle);

            return DownloadFile;
        }