ASP.NET

function checkFile(what, mb, iLen, types) {
   // what  : always =this in calling function
   // mb    : max file size allowed in MB
   // iLen  : max length of filename allowed (excluding the extension); 0 means don't test for length
   // types : comma-delimited string of allowed file extensions
   // eg, call with onchange="checkFile(this,3,50,'doc,docx,pdf')"
   var msg = '';
   var source = what.value;
   var i = source.lastIndexOf('\');
   var j = source.lastIndexOf('.');
   var fName = source.substring(i + 1, j);
   var ext = source.substring(source.lastIndexOf(".") + 1, source.length).toLowerCase();
   var exts = types.split(',');
   var fileTypeAllowed = false;
   for (var k = 0; k < exts.length; k++) {
      if (ext == exts[k]) {
         fileTypeAllowed = true;
         break;
      }
   }
   if (fileTypeAllowed == true) {
      var regex = /^[A-Za-z0-9_ -]{1,1024}$/;
      if (!regex.test(fName)) {
         msg = 'The file name contains illegal characters\n  Please re-name the file using only alphanumeric characters, hyphens, spaces and underscores\n';
      }
   } else {
      msg = 'Please upload files of the following types only:\n  ' + types + '\n';
   }
   if ((iLen > 0) && (fName.length > iLen)) {
      msg += 'The file name is too long\n  Please restrict it to ' + iLen.toString() + ' characters.\n';
   }
   var fileSize = what.files[0].size;
   var iMax = mb * 1024 * 1000;
   if (!((fileSize > 0) && (fileSize <= iMax))) {
      msg += "The file size should be greater than 0 and less than " + mb.toString() + "MB\n";
   }
   if (!(msg == '')) { what.value = null; alert(msg + '\n' + fName + '.' + ext); }
}

Dim sUrl As String = Request.Url.ToString.ToLower
If Request.ContentLength > 4096000 Then 
    Response.Redirect([full path to some nice error page])
End If

protected void Page_Load(object sender, EventArgs e)
        {
            Investigator _objInvestigator = new Investigator();
            InvestigatorService _objinvestigatorService = new InvestigatorService();

            int InvestigatorId;
            InvestigatorId = ((Session["InvestigatorId"] != null) && int.TryParse(Session["InvestigatorId"].ToString(), out InvestigatorId)) ? InvestigatorId : 0;
            _objInvestigator = _objinvestigatorService.GetByInvestigatorId(InvestigatorId);
            if (_objInvestigator != null)
            {
                if ((_objInvestigator.CvFile != null) && !string.IsNullOrEmpty(_objInvestigator.CvFileNameWithExt))
                {
                    String ext = System.IO.Path.GetExtension(_objInvestigator.CvFileNameWithExt);

                        Response.ContentType = "application/" + ext;
                        Response.AddHeader("content-length", _objInvestigator.CvFile.Length.ToString());
                        Response.BinaryWrite(_objInvestigator.CvFile);

                }
            }

        }  

protected void loadFile_Click(object sender, EventArgs e)
       {
           Response.Write(string.Format("<script>window.open('{0}','_blank');</script>", "TheFile.aspx"));
       }

Investigator _objInvestigator = new Investigator();
            InvestigatorService _objinvestigatorService = new InvestigatorService();

            int InvestigatorId;
            InvestigatorId = ((Session["InvestigatorId"] != null) && int.TryParse(Session["InvestigatorId"].ToString(), out InvestigatorId)) ? InvestigatorId : 0;
            _objInvestigator = _objinvestigatorService.GetByInvestigatorId(InvestigatorId);
            if (_objInvestigator != null)
            {
                if ((_objInvestigator.CvFile != null) && !string.IsNullOrEmpty(_objInvestigator.CvFileNameWithExt))
                {
                    String ext = System.IO.Path.GetExtension(_objInvestigator.CvFileNameWithExt);

                    //string path = Server.MapPath("~\E:\karthikeyan\venky\pdf\aaaa.PDF");
                    //WebClient client = new WebClient();
                    //Byte[] buffer = client.DownloadData(path);
                    //if (buffer != null)
                    //{

                    if (ext.ToLower() == ".doc")
                    {
                        Response.ContentType = "application/" + "msword";
                        Response.AddHeader("content-length", _objInvestigator.CvFile.Length.ToString());
                        Response.BinaryWrite(_objInvestigator.CvFile);
                    }
                    else if(ext.ToLower() == ".docx")
                    {
                        Response.ContentType = "application/" + "vnd.openxmlformats-officedocument.wordprocessingml.document";
                        Response.AddHeader("content-length", _objInvestigator.CvFile.Length.ToString());
                        Response.BinaryWrite(_objInvestigator.CvFile);
                    }
                    else if (ext.ToLower() == ".pdf")
                    {
                        Response.ContentType = "application/" + ext;
                        Response.AddHeader("content-length", _objInvestigator.CvFile.Length.ToString());
                        Response.BinaryWrite(_objInvestigator.CvFile);
                    }

                }
            }