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Value cannot be null. Parameter name: elementId in PDFsharp

I am working on Export to PDF funtionality using C# and PDFSharp. I am getting this error:
Value cannot be null.
Parameter name: elementId
The error is on this line :
PdfDocument document = PdfGenerator.GeneratePdf(htmlcontenttbl.ToString(), PdfSharp.PageSize.A4, 30);
Here's the whole method:
public bool ExportPdf(string htmlcontenttbl)
{
Response.ClearContent();
Response.ClearHeaders();
Response.Buffer = true;
Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", "attachment;filename=Myfile.pdf");
//Response.AddHeader("Content-Disposition", "inline;filename=file.pdf");
//Response.AppendHeader("Content-Disposition", "attachment; filename=Myfile.pdf");
Response.Charset = "";
StringWriter sw = new StringWriter();
HtmlTextWriter htw = new HtmlTextWriter(sw);
PdfDocument document = PdfGenerator.GeneratePdf(htmlcontenttbl.ToString(), PdfSharp.PageSize.A4, 30);
var config = new PdfGenerateConfig();
config.PageOrientation = PageOrientation.Landscape;
config.PageSize = PageSize.A4;
config.MarginBottom = 30;
config.MarginTop = 30;
//PdfDocument document = PdfGenerator.GeneratePdf(htmlcontenttbl, config);
byte[] bytes = null;
using (MemoryStream stream = new MemoryStream())
{
document.Save(stream, true);
bytes = stream.ToArray();
}
//var path1 = Server.MapPath("~/Images/" + DateTime.Now.TimeOfDay.Ticks + "result.pdf");
//System.IO.File.WriteAllBytes(path1, bytes);
//Response.TransmitFile(path1, 0, bytes.Length);
//Response.OutputStream.Write(bytes, 0, bytes.Length);
Response.BinaryWrite(bytes);
Response.Flush();
Response.End();
return true;
}

That exception can occur if you have a blank anchor tag.
It is likely ultimately being generated from here.
You should remove the blank anchor tag.

ASP.NET convert and download pdf using ClosedXML and Spire.XLS

I use Web Forms. I try to convert ClosedXML excel workbook to pdf using Spire.XLS and download it by a client.
Here is my code:
protected void btnExport_OnClick(object sender, EventArgs e)
{
var excel = Reporting.GenerateExcel(); //custom, return XLWorkbook object
string myName = Server.UrlEncode(121 + "_" + DateTime.Now.ToShortDateString() + ".xlsx");
MemoryStream stream = GetStream(excel);
MemoryStream stream1 = new MemoryStream();
Workbook book = new Workbook();
book.LoadFromStream(stream);
book.SaveToStream(stream1, FileFormat.PDF);
Response.Clear();
Response.Buffer = true;
Response.AddHeader("content-disposition", "attachment; filename=" + myName);
Response.ContentType = "application/pdf";
Response.BinaryWrite(stream1.ToArray());
Response.End();
}
public MemoryStream GetStream(XLWorkbook excelWorkbook)
{
MemoryStream fs = new MemoryStream();
excelWorkbook.SaveAs(fs);
fs.Position = 0;
return fs;
}
It seems like I receive not correct pdf. Thanks

Adding text a pdf while downloading (streaming) from ftp with itextsharp

I have some code for showing pdf files in browser that come from ftp. I have to add some text to pdf that come from ftp. And I found some working codes for it from antoher projects but it writes to pdf from iis local path.
//** these are my working code that show pdf files in browser from ftp. **//
string filename = Request.QueryString["view"];
string ftpServerIP = Session["Host"].ToString();
string ftpUserName = Session["user"].ToString();
string ftpPassword = Session["pssw"].ToString();
FileInfo objFile = new FileInfo(filename);
System.Net.FtpWebRequest request = (System.Net.FtpWebRequest)WebRequest.Create(new Uri("ftp://" + ftpServerIP + "/" + objFile.Name));
request.Credentials = new NetworkCredential(SftpUserName, ftpPassword);
request.Method = WebRequestMethods.Ftp.GetFileSize;
System.Net.FtpWebResponse response = (System.Net.FtpWebResponse)request.GetResponse();
int length = (int)(response.ContentLength * 1.1);
request = (System.Net.FtpWebRequest)WebRequest.Create(new Uri("ftp://" + ftpServerIP + "/" + objFile.Name));
request.Credentials = new NetworkCredential(ftpUserName, ftpPassword);
request.Method = WebRequestMethods.Ftp.DownloadFile;
response = (System.Net.FtpWebResponse)request.GetResponse();
Stream responseStream = response.GetResponseStream();
StreamReader reader = new StreamReader(responseStream);
BinaryReader br = new BinaryReader(responseStream);
byte[] buffer = br.ReadBytes(length);
//** Can I work the itextsharp codes near here for adding text, without saving local, before download? **//
Response.Clear();
Response.ClearHeaders();
Response.ClearContent();
Response.ContentEncoding = reader.CurrentEncoding;
Response.ContentType = "application/pdf";
Response.AddHeader("Content-Disposition", "inline; filename=" + Request.QueryString["name"]);
Response.BinaryWrite(buffer);
//** these are another code which I need to implement my code for adding some text in pdf files.**//
//** these are not my actual codes, just from another project's and I have to use them in my project.**//
//** The difference is in my project download pdf directly from an ftp, other one reads pdf in local files.**//
private void WriteToPdf(FileInfo sourceFile, string outbut_File, string stringToWriteToPdf)
{
PdfReader reader = new PdfReader(sourceFile.FullName);
PdfStamper pdfStamper = new PdfStamper(reader, new System.IO.FileStream(outbut_File, FileMode.Create, FileAccess.Write, FileShare.Write));
iTextSharp.text.pdf.PdfGState Gstates = new iTextSharp.text.pdf.PdfGState();
Gstates.StrokeOpacity = 0.3f;
Gstates.FillOpacity = 0.3f;
for (int i = 1; i <= reader.NumberOfPages; i++)
{
iTextSharp.text.Rectangle pageSize = reader.GetPageSizeWithRotation(i);
PdfContentByte pdfPageContents = pdfStamper.GetOverContent(i);
pdfPageContents.BeginText();
BaseFont baseFont__1 = BaseFont.CreateFont(BaseFont.HELVETICA_BOLD, BaseFont.WINANSI, BaseFont.NOT_EMBEDDED);
//BaseFont.CreateFont("", BaseFont.WINANSI, BaseFont.NOT_EMBEDDED)
pdfPageContents.SetFontAndSize(baseFont__1, 15);
pdfPageContents.SetRGBColorFill(255, 0, 0);
pdfPageContents.SaveState();
float textAngle = 0;
pdfPageContents.ShowTextAligned(PdfContentByte.ALIGN_LEFT, stringToWriteToPdf, 5, 5, textAngle);
pdfPageContents.ShowTextAligned(PdfContentByte.ALIGN_LEFT, stringToWriteToPdf, pageSize.Width, pageSize.Height, textAngle);
pdfPageContents.EndText();
}
pdfStamper.FormFlattening = true;
pdfStamper.Close();
reader.Close();
Stream s = File.OpenRead(outbut_File);
byte[] buffer = new byte[s.Length + 1];
try
{
s.Read(buffer, 0, (Int32)s.Length);
}
finally
{
s.Close();
}
Response.ClearContent();
Response.ContentType = "application/pdf";
Response.AddHeader("Content-Disposition", "inline; filename=" + Request.QueryString["name"]);
Response.WriteFile(outbut_File);
Response.End();
}
How should I customise these codes from downloading ftp and adding text then showing in browser?

Edit pdf itextsharp and send to the browser

I want to edit and existing pdf and to send the result to the broswer
Here is my methode:
public static byte[] Generate()
{
var templatePath = HttpContext.Current.Server.MapPath("~/my_template.pdf");
// Based on:
// http://www.johnnycode.com/blog/2010/03/05/using-a-template-to-programmatically-create-pdfs-with-c-and-itextsharp/
var reader = new PdfReader(templatePath);
var outStream = new MemoryStream();
var stamper = new PdfStamper(reader, outStream);
var form = stamper.AcroFields;
var fieldKeys = form.Fields.Keys;
foreach (string fieldKey in fieldKeys)
{
if (form.GetField(fieldKey) == "MyTemplatesOriginalTextFieldA")
form.SetField(fieldKey, "1234");
if (form.GetField(fieldKey) == "MyTemplatesOriginalTextFieldB")
form.SetField(fieldKey, "5678");
}
// "Flatten" the form so it wont be editable/usable anymore
stamper.FormFlattening = true;
stamper.Close();
reader.Close();
return outStream.ToArray();
}
and
The method call
byte[] buffer = Generate();
Response.ContentType = "application/pdf";
Response.AddHeader("content-length", buffer.Length.ToString());
Response.BinaryWrite(buffer);
Can someone help me in this case ?

Add this line
byte[] buffer = Generate();
Response.ContentType = "application/pdf";
Response.AddHeader("content-length", buffer.Length.ToString());
Response.AppendHeader("Content-Disposition", "attachment; filename=youPDFName.pdf");
Response.BinaryWrite(buffer);
Response.End();
I have added Content-Disposition and response.end in code.
tested above code , work fine. let me know if it works you.

Reponds.appendHeader not work on IE

i m using C#.
with this syntax Response.AppendHeader("REFRESH", "2;URL=../Ordres.aspx"); work on Firefox and Chrome
using (MemoryStream ms = new MemoryStream())
{
try
{
PdfExportOptions opts = new PdfExportOptions();
opts.ShowPrintDialogOnOpen = true;
xtraReport_Pricipal.ExportToPdf(ms, opts);
ms.Seek(0, SeekOrigin.Begin);
byte[] report = ms.ToArray();
Page.Response.ContentType = "application/pdf";
Page.Response.Clear();
Page.Response.OutputStream.Write(report, 0, report.Length);
HttpContext.Current.ApplicationInstance.CompleteRequest();
}
finally
{
ms.Close();
}
}
Response.AppendHeader("REFRESH", "2;URL=../Ordres.aspx");
but not on Internet explorer. how can i redirect the page after 2 sec on IE ?
Thanks in advance

use
response.AppendHeader("Content-Disposition", string.Format("attachment;filename={0}", fileName));