How Do I Convert Div Region Into Pdf And Excel Format Using C# In Offline

you can use iTextSharp to generate PDF file. use package manager to install it.
https://www.nuget.org/packages/itextsharp/[^]

<div id="MyDiv"  runat="server">
<p>div content</p>
</div>

in your code, for example button click event:

protected void btnExport_Click(object sender, EventArgs e)
{
    Response.ContentType = "application/pdf";
    Response.AddHeader("content-disposition", "attachment;filename=div.pdf");
    Response.Cache.SetCacheability(HttpCacheability.NoCache);
   
    StringWriter stringWriter = new StringWriter();
    HtmlTextWriter htmlTextWriter = new HtmlTextWriter(stringWriter);
    MyDiv.RenderControl(htmlTextWriter);
   
    StringReader stringReader = new StringReader(stringWriter.ToString());
    Document Doc = new Document(PageSize.A4, 10f, 10f, 100f, 0f);
    HTMLWorker htmlparser = new HTMLWorker(Doc);
    PdfWriter.GetInstance(Doc, Response.OutputStream);
   
    Doc.Open();
    htmlparser.Parse(stringReader);
    Doc.Close();
    Response.Write(Doc);
    Response.End();
}

you need to add below using statements at the top of your c# code

using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.text.html;
using iTextSharp.text.html.simpleparser;