Creating a PDF from a RDLC Report in the Background

This is easy to do, you can render the report as a PDF, and save the resulting byte array as a PDF file on disk. To do this in the background, that's more a question of how your app is written. You can just spin up a new thread, or use a BackgroundWorker (if this is a WinForms app), etc. There, of course, may be multithreading issues to be aware of.

Warning[] warnings;
string[] streamids;
string mimeType;
string encoding;
string filenameExtension;

byte[] bytes = reportViewer.LocalReport.Render(
    "PDF", null, out mimeType, out encoding, out filenameExtension,
    out streamids, out warnings);

using (FileStream fs = new FileStream("output.pdf", FileMode.Create))
{
    fs.Write(bytes, 0, bytes.Length);
}

You can use following code which generate pdf file in background as like on button click and then would popup in brwoser with SaveAs and cancel option.

Warning[] warnings;
        string[] streamIds;
        string mimeType = string.Empty;
        string encoding = string.Empty;`enter code here`
        string extension = string.Empty;
        DataSet dsGrpSum, dsActPlan, dsProfitDetails,
            dsProfitSum, dsSumHeader, dsDetailsHeader, dsBudCom = null;

    enter code here

//This is optional if you have parameter then you can add parameters as much as you want
ReportParameter[] param = new ReportParameter[5];
            param[0] = new ReportParameter("Report_Parameter_0", "1st Para", true);
            param[1] = new ReportParameter("Report_Parameter_1", "2nd Para", true);
            param[2] = new ReportParameter("Report_Parameter_2", "3rd Para", true);
            param[3] = new ReportParameter("Report_Parameter_3", "4th Para", true);
            param[4] = new ReportParameter("Report_Parameter_4", "5th Para");

            DataSet  dsData= "Fill this dataset with your data";
            ReportDataSource rdsAct = new ReportDataSource("RptActDataSet_usp_GroupAccntDetails", dsActPlan.Tables[0]);
            ReportViewer viewer = new ReportViewer();
            viewer.LocalReport.Refresh();
            viewer.LocalReport.ReportPath = "Reports/AcctPlan.rdlc"; //This is your rdlc name.
            viewer.LocalReport.SetParameters(param);
            viewer.LocalReport.DataSources.Add(rdsAct); // Add  datasource here         
            byte[] bytes = viewer.LocalReport.Render("PDF", null, out mimeType, out encoding, out extension, out streamIds, out warnings);
            // byte[] bytes = viewer.LocalReport.Render("Excel", null, out mimeType, out encoding, out extension, out streamIds, out warnings);
            // Now that you have all the bytes representing the PDF report, buffer it and send it to the client.          
            // System.Web.HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.NoCache);
            Response.Buffer = true;
            Response.Clear();
            Response.ContentType = mimeType;
            Response.AddHeader("content-disposition", "attachment; filename= filename" + "." + extension);
            Response.OutputStream.Write(bytes, 0, bytes.Length); // create the file  
            Response.Flush(); // send it to the client to download  
            Response.End();

You don't need to have a reportViewer control anywhere - you can create the LocalReport on the fly:

var lr = new LocalReport
{
    ReportPath = Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location) ?? @"C:\", "Reports", "PathOfMyReport.rdlc"),
    EnableExternalImages = true
};

lr.DataSources.Add(new ReportDataSource("NameOfMyDataSet", model));

string mimeType, encoding, extension;

Warning[] warnings;
string[] streams;
var renderedBytes = lr.Render
    (
        "PDF",
        @"<DeviceInfo><OutputFormat>PDF</OutputFormat><HumanReadablePDF>False</HumanReadablePDF></DeviceInfo>",
        out mimeType,
        out encoding,
        out extension,
        out streams,
        out warnings
    );

var saveAs = string.Format("{0}.pdf", Path.Combine(tempPath, "myfilename"));

var idx = 0;
while (File.Exists(saveAs))
{
    idx++;
    saveAs = string.Format("{0}.{1}.pdf", Path.Combine(tempPath, "myfilename"), idx);
}

using (var stream = new FileStream(saveAs, FileMode.Create, FileAccess.Write))
{
    stream.Write(renderedBytes, 0, renderedBytes.Length);
    stream.Close();
}

lr.Dispose();

You can also add parameters: (lr.SetParameter()), handle subreports: (lr.SubreportProcessing+=YourHandler), or pretty much anything you can think of.

The below code work fine with me of sure thanks for the above comments. You can add report viewer and change the visible=false and use the below code on submit button:

protected void Button1_Click(object sender, EventArgs e)
{
    Warning[] warnings;
    string[] streamIds;
    string mimeType = string.Empty;
    string encoding = string.Empty;
    string extension = string.Empty;
    string HIJRA_TODAY = "01/10/1435";
    ReportParameter[] param = new ReportParameter[3];
    param[0] = new ReportParameter("CUSTOMER_NUM", CUSTOMER_NUMTBX.Text);
    param[1] = new ReportParameter("REF_CD", REF_CDTB.Text);
    param[2] = new ReportParameter("HIJRA_TODAY", HIJRA_TODAY);

    byte[] bytes = ReportViewer1.LocalReport.Render(
        "PDF", 
        null, 
        out mimeType, 
        out encoding, 
        out extension, 
        out streamIds, 
        out warnings);

    Response.Buffer = true;
    Response.Clear();
    Response.ContentType = mimeType;
    Response.AddHeader(
        "content-disposition", 
        "attachment; filename= filename" + "." + extension);
    Response.OutputStream.Write(bytes, 0, bytes.Length); // create the file  
    Response.Flush(); // send it to the client to download  
    Response.End();
}    

 private void PDFExport(LocalReport report)
    {           
        string[] streamids;
        string minetype;
        string encod;
        string fextension;
        string deviceInfo =
          "<DeviceInfo>" +
          "  <OutputFormat>EMF</OutputFormat>" +
          "  <PageWidth>8.5in</PageWidth>" +
          "  <PageHeight>11in</PageHeight>" +
          "  <MarginTop>0.25in</MarginTop>" +
          "  <MarginLeft>0.25in</MarginLeft>" +
          "  <MarginRight>0.25in</MarginRight>" +
          "  <MarginBottom>0.25in</MarginBottom>" +
          "</DeviceInfo>";
        Warning[] warnings;
        byte[] rpbybe = report.Render("PDF", deviceInfo, out minetype, out encod, out fextension, out streamids,
           out warnings);
        using(FileStream fs=new FileStream("E:\\newwwfg.pdf",FileMode.Create))
        {
            fs.Write(rpbybe , 0, rpbybe .Length);
        }

}