Hi Fahimahmed, 

 Pleaser refer below sample.

HTML Page

<img src="https://www.aspsnippets.com/images/Blue/Logo.png" alt="Alternate Text" />
<br />
<br />
<div>
    <div style="border-top: 3px solid #22BCE5">
        &nbsp;
    </div>
    <span class="btn btn-info">
        Hello <b>{UserName}</b>
        <br /><br />
        A new article has been published on ASPSnippets.
        <br />
        <a style="color: #22BCE5" href="{Url}">{Title}</a><br />
        {Description}
        <br /><br />
        Thanks<br />
        ASPSnippets
    </span>
</div>

HTML

<asp:Button Text="Export" ID="btnExport" runat="server" OnClick="Export" />

Namespaces

C#

using System.IO;
using System.Text;
using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.tool.xml.parser;
using iTextSharp.tool.xml;
using iTextSharp.tool.xml.pipeline.css;
using iTextSharp.tool.xml.pipeline.html;
using iTextSharp.tool.xml.html;
using iTextSharp.tool.xml.pipeline.end;

VB.Net

Imports System.IO
Imports System.Text
Imports iTextSharp.text
Imports iTextSharp.text.pdf
Imports iTextSharp.tool.xml.parser
Imports iTextSharp.tool.xml
Imports iTextSharp.tool.xml.pipeline.css
Imports iTextSharp.tool.xml.pipeline.html
Imports iTextSharp.tool.xml.html
Imports iTextSharp.tool.xml.pipeline.end

Code

C#

protected void Export(object sender, EventArgs e)
{
    string body = string.Empty;
    using (StreamReader reader = new StreamReader(Server.MapPath("~/EmailTemplate.html")))
    {
        body = reader.ReadToEnd();
    }
    body = body.Replace("{UserName}", "Mudassar");
    body = body.Replace("{Title}", "Convert HTML File to PDF using C# and VB.Net in ASP.Net");
    body = body.Replace("{Url}", "https://www.aspsnippets.com/Articles/Send-Email-using-HTML-Templates-in-ASPNet-with-C-and-VBNet.aspx");
    body = body.Replace("{Description}", "Here Mudassar Ahmed Khan has explained with an example, how to send Email using HTML Templates in ASP.Net with C# and VB.Net.");
    byte[] byteArray = Encoding.UTF8.GetBytes(body);
    using (StringWriter sw = new StringWriter())
    {
        using (HtmlTextWriter hw = new HtmlTextWriter(sw))
        {
            using (StreamReader sr = new StreamReader(new MemoryStream(byteArray)))
            {
                Document pdfDoc = new Document(PageSize.A2, 80f, 80f, 80f, 80f);
                PdfWriter PdfWriter = PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
                HtmlPipelineContext htmlContext = new HtmlPipelineContext(null);
                htmlContext.SetTagFactory(Tags.GetHtmlTagProcessorFactory());
                ICSSResolver cssResolver = XMLWorkerHelper.GetInstance().GetDefaultCssResolver(false);
                cssResolver.AddCssFile("https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css", true);
                IPipeline pipeline = new CssResolverPipeline(cssResolver, new HtmlPipeline(htmlContext, new PdfWriterPipeline(pdfDoc, PdfWriter)));
                var worker = new XMLWorker(pipeline, true);
                var xmlParse = new XMLParser(true, worker);
                pdfDoc.Open();
                xmlParse.Parse(sr);
                xmlParse.Flush();
                pdfDoc.Close();
                Response.ContentType = "application/pdf";
                Response.AddHeader("content-disposition", "attachment;filename=HTMLExport.pdf");
                Response.Cache.SetCacheability(HttpCacheability.NoCache);
                Response.Write(pdfDoc);
                Response.End();
            }
        }
    }
}

VB.Net

Protected Sub Export(ByVal sender As Object, ByVal e As EventArgs)
    Dim body As String = String.Empty
    Using reader As StreamReader = New StreamReader(Server.MapPath("~/EmailTemplate.html"))
        body = reader.ReadToEnd()
    End Using
    body = body.Replace("{UserName}", "Mudassar")
    body = body.Replace("{Title}", "Convert HTML File to PDF using C# and VB.Net in ASP.Net")
    body = body.Replace("{Url}", "https://www.aspsnippets.com/Articles/Send-Email-using-HTML-Templates-in-ASPNet-with-C-and-VBNet.aspx")
    body = body.Replace("{Description}", "Here Mudassar Ahmed Khan has explained with an example, how to send Email using HTML Templates in ASP.Net with C# and VB.Net.")
    Dim byteArray As Byte() = Encoding.UTF8.GetBytes(body)
    Using sw As StringWriter = New StringWriter()
        Using hw As HtmlTextWriter = New HtmlTextWriter(sw)
            Using sr As StreamReader = New StreamReader(New MemoryStream(byteArray))
                Dim pdfDoc As Document = New Document(PageSize.A2, 80.0F, 80.0F, 80.0F, 80.0F)
                Dim PdfWriter As PdfWriter = PdfWriter.GetInstance(pdfDoc, Response.OutputStream)
                Dim htmlContext As HtmlPipelineContext = New HtmlPipelineContext(Nothing)
                htmlContext.SetTagFactory(Tags.GetHtmlTagProcessorFactory())
                Dim cssResolver As ICSSResolver = XMLWorkerHelper.GetInstance().GetDefaultCssResolver(False)
                cssResolver.AddCssFile("https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css", True)
                Dim pipeline As IPipeline = New CssResolverPipeline(cssResolver, New HtmlPipeline(htmlContext, New PdfWriterPipeline(pdfDoc, PdfWriter)))
                Dim worker = New XMLWorker(pipeline, True)
                Dim xmlParse = New XMLParser(True, worker)
                pdfDoc.Open()
                xmlParse.Parse(sr)
                xmlParse.Flush()
                pdfDoc.Close()
                Response.ContentType = "application/pdf"
                Response.AddHeader("content-disposition", "attachment;filename=HTMLExport.pdf")
                Response.Cache.SetCacheability(HttpCacheability.NoCache)
                Response.Write(pdfDoc)
                Response.End()
            End Using
        End Using
    End Using
End Sub

 Screenshot

Hi fahimahmed,

 Please refer below Sample.

Database

I have made use of the following table Customers with the schema as follows. 

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.

Download SQL file

HTML Page

<div class="container-fluid">
    <div class="row" style="padding:40px 40px 5px 50px;">
        <div class="row">
            <div class="col-sm-12" style="padding:5px; ">
                <div class="card bg-light">
                    <div class="card-body" style="text-align:center;height:100px; margin-top:-10px;">
                        <img src="https://w7.pngwing.com/pngs/786/126/png-transparent-logo-contracting-photography-logo-symbol.png" height="50" width="100" />
                        <p style="font-size:8px; margin-top:5px;">Warehouse # 3, Industrial Area 15, Sharjah - UAE</p>
                        <p style="font-size:8px; margin-top:-15px; "><i class="bi bi-telephone-inbound"></i> +971 50 5221797 | <i class="bi bi-envelope"></i> info@shipments.care | <i class="bi bi-globe"></i> https://shipments.care</p>
                    </div>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-sm-4" style="padding:5px;">
                <div class="card bg-light" style="text-align:center;">
                    <div class="card-header" style="padding:1px; font-size:10px; text-align:center;">WayBill #</div>
                    <div class="card-body">
                        <p class="card-text" style="padding:5px; margin-left:-15px; font-family: IDAutomationHC39M; font-size:medium;">1</p>
                    </div>
                </div>
            </div>
            <div class="col-sm-4" style="padding:5px;">
                <div class="card bg-light" style="text-align:center;">
                    <div class="card-header" style="padding:1px; font-size:10px; text-align:center;">Reference #</div>
                    <div class="card-body">
                        <p class="card-text" style="padding:5px; margin-left:-15px; font-family: IDAutomationHC39M; font-size:small;">1</p>
                    </div>
                </div>
            </div>
            <div class="col-sm-4" style="padding:5px;">
                <div class="card bg-light" style="text-align:center;">
                    <div class="card-header" style="padding:1px; font-size:10px; text-align:center;">Courier: DTDC</div>
                    <div class="card-body">
                        <p class="card-text" style="padding: 5px; margin-left: -15px; font-family: IDAutomationHC39M; font-size: small;">1</p>
                    </div>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-sm-6" style="padding:5px;">
                <div class="card bg-light">
                    <div class="card-header" style="padding:1px; font-size:10px; text-align:center;">SENDER</div>
                    <div class="card-body" style="padding:5px 10px 5px 10px">
                        <div class="card-text" style="font-size:10px;">
                            <table>
                                <tr>
                                    <td class="tableheading">Customer Id </td>
                                    <td>:</td>
                                    <td class="tablerows">{CustomerId}</td>
                                </tr>
                                <tr>
                                    <td class="tableheading">Name</td>
                                    <td>:</td>
                                    <td class="tablerows">{Name}</td>
                                </tr>
                                <tr>
                                    <td class="tableheading">Country</td>
                                    <td>:</td>
                                    <td class="tablerows OverflowText">{Country}</td>
                                </tr>
                            </table>
                        </div>
                    </div>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-sm-12">
                <footer class="blockquote-footer" style="font-size:10px; padding-left:10px;">Generated on {Date_Time}</footer>
            </div>
        </div>
    </div>
</div>

HTML

<asp:GridView runat="server" ID="gvCustomers" AutoGenerateColumns="false" CssClass="table table-responsive" HeaderStyle-BackColor="#3AC0F2"
    HeaderStyle-ForeColor="White" RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White"
    AlternatingRowStyle-ForeColor="#000" AllowPaging="true" PageSize="1">
    <Columns>
        <asp:BoundField DataField="CustomerId" HeaderText="ID" ItemStyle-Width="150px" />
        <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="150px" />
        <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150px" />
    </Columns>
</asp:GridView>
<br />
<asp:Button Text="Export" ID="btnExport" runat="server" OnClick="Export" />

Namespaces

C#

using System.Data.SqlClient;
using System.Data;
using System.Configuration;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.tool.xml.parser;
using iTextSharp.tool.xml;
using iTextSharp.tool.xml.pipeline.css;
using iTextSharp.tool.xml.pipeline.html;
using iTextSharp.tool.xml.html;
using iTextSharp.tool.xml.pipeline.end;

VB.Net

Imports System.Data.SqlClient
Imports System.Data
Imports System.Configuration
Imports System.IO
Imports iTextSharp.text
Imports iTextSharp.text.pdf
Imports iTextSharp.tool.xml.parser
Imports iTextSharp.tool.xml
Imports iTextSharp.tool.xml.pipeline.css
Imports iTextSharp.tool.xml.pipeline.html
Imports iTextSharp.tool.xml.html
Imports iTextSharp.tool.xml.pipeline.end

Code

c#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.BindGrid();
    }
}

protected void Export(object sender, EventArgs e)
{
    Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 10f);
    PdfWriter writer = PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
    HtmlPipelineContext htmlContext = new HtmlPipelineContext(null);
    htmlContext.SetTagFactory(Tags.GetHtmlTagProcessorFactory());
    ICSSResolver cssResolver = XMLWorkerHelper.GetInstance().GetDefaultCssResolver(false);
    cssResolver.AddCssFile(Server.MapPath("~/Barcode.css"), true);
    IPipeline pipeline = new CssResolverPipeline(cssResolver, new HtmlPipeline(htmlContext, new PdfWriterPipeline(pdfDoc, writer)));
    var worker = new XMLWorker(pipeline, true);
    var xmlParse = new XMLParser(true, worker);
    pdfDoc.Open();
    for (int i = 0; i < gvCustomers.PageCount; i++)
    {
        using (StringWriter sw = new StringWriter())
        {
            using (HtmlTextWriter hw = new HtmlTextWriter(sw))
            {
                gvCustomers.PageIndex = i;
                gvCustomers.PagerSettings.Visible = false;
                this.BindGrid();
                gvCustomers.RenderControl(hw);
                string body = string.Empty;
                using (StreamReader reader = new StreamReader(Server.MapPath("~/EmailTemplate.html")))
                {
                    body = reader.ReadToEnd();
                }
                body = body.Replace("{CustomerId}", gvCustomers.Rows[0].Cells[0].Text);
                body = body.Replace("{Name}", gvCustomers.Rows[0].Cells[1].Text);
                body = body.Replace("{Country}", gvCustomers.Rows[0].Cells[2].Text);
                body = body.Replace("{Date_Time}", DateTime.Now.ToString("dd/MM/yyyy"));
                body += "<br /><br />";
                StringReader sr = new StringReader(body + "<br /><br />" + sw.ToString());
                pdfDoc.NewPage();
                xmlParse.Parse(sr);
            }
        }
    }
    xmlParse.Flush();
    pdfDoc.Close();
    gvCustomers.PagerSettings.Visible = true;
    Response.ContentType = "application/pdf";
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.pdf");
    Response.Cache.SetCacheability(HttpCacheability.NoCache);
    Response.Write(pdfDoc);
    Response.End();
}

public override void VerifyRenderingInServerForm(Control control)
{

}

private void BindGrid()
{
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT CustomerId, Name, Country FROM Customers", con))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    gvCustomers.DataSource = dt;
                    gvCustomers.DataBind();
                }
            }
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    If Not Me.IsPostBack Then
        Me.BindGrid()
    End If
End Sub

Protected Sub Export(ByVal sender As Object, ByVal e As EventArgs)
    Dim pdfDoc As Document = New Document(PageSize.A4, 10.0F, 10.0F, 10.0F, 10.0F)
    Dim writer As PdfWriter = PdfWriter.GetInstance(pdfDoc, Response.OutputStream)
    Dim htmlContext As HtmlPipelineContext = New HtmlPipelineContext(Nothing)
    htmlContext.SetTagFactory(Tags.GetHtmlTagProcessorFactory())
    Dim cssResolver As ICSSResolver = XMLWorkerHelper.GetInstance().GetDefaultCssResolver(False)
    cssResolver.AddCssFile(Server.MapPath("~/Barcode.css"), True)
    Dim pipeline As IPipeline = New CssResolverPipeline(cssResolver, New HtmlPipeline(htmlContext, New PdfWriterPipeline(pdfDoc, writer)))
    Dim worker = New XMLWorker(pipeline, True)
    Dim xmlParse = New XMLParser(True, worker)
    pdfDoc.Open()
    For i As Integer = 0 To gvCustomers.PageCount - 1
        Using sw As StringWriter = New StringWriter()
            Using hw As HtmlTextWriter = New HtmlTextWriter(sw)
                gvCustomers.PageIndex = i
                gvCustomers.PagerSettings.Visible = False
                Me.BindGrid()
                gvCustomers.RenderControl(hw)
                Dim body As String = String.Empty
                Using reader As StreamReader = New StreamReader(Server.MapPath("~/EmailTemplate.html"))
                    body = reader.ReadToEnd()
                End Using
                body = body.Replace("{CustomerId}", gvCustomers.Rows(0).Cells(0).Text)
                body = body.Replace("{Name}", gvCustomers.Rows(0).Cells(1).Text)
                body = body.Replace("{Country}", gvCustomers.Rows(0).Cells(2).Text)
                body = body.Replace("{Date_Time}", DateTime.Now.ToString("dd/MM/yyyy"))
                body += "<br /><br />"
                Dim sr As StringReader = New StringReader(body & "<br /><br />" & sw.ToString())
                pdfDoc.NewPage()
                xmlParse.Parse(sr)
            End Using
        End Using
    Next

    xmlParse.Flush()
    pdfDoc.Close()
    gvCustomers.PagerSettings.Visible = True
    Response.ContentType = "application/pdf"
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.pdf")
    Response.Cache.SetCacheability(HttpCacheability.NoCache)
    Response.Write(pdfDoc)
    Response.End()
End Sub

Public Overrides Sub VerifyRenderingInServerForm(ByVal control As Control)
End Sub

Private Sub BindGrid()
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(conString)
        Using cmd As SqlCommand = New SqlCommand("SELECT CustomerId, Name, Country FROM Customers", con)
            Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                Using dt As DataTable = New DataTable()
                    sda.Fill(dt)
                    gvCustomers.DataSource = dt
                    gvCustomers.DataBind()
                End Using
            End Using
        End Using
    End Using
End Sub