Hi ibalochie,

Check the below sample. In this sample i have send id as file name. You need to replace id with invoiceno as file name.

HTML

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" />
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:BoundField DataField="Country" HeaderText="Country" />
    </Columns>
</asp:GridView>
<br />
<asp:Button Text="Send Email" runat="server" OnClick="OnSend" />

Namespaces

C#

using System.Data;
using System.IO;
using System.Net.Mail;
using iTextSharp.text;
using iTextSharp.text.pdf;

VB.Net

Imports System.Data
Imports System.IO
Imports System.Net.Mail
Imports iTextSharp.text
Imports iTextSharp.text.pdf

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] {
            new DataColumn("Id"),
            new DataColumn("Name"),
            new DataColumn("Country") });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

protected void OnSend(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.Add(new DataColumn("Id", typeof(string)));
    dt.Columns.Add(new DataColumn("Data", typeof(byte[])));

    foreach (GridViewRow row in GridView1.Rows)
    {
        string id = row.Cells[0].Text.Trim();
        string name = row.Cells[1].Text.Trim();
        string country = row.Cells[2].Text.Trim();
        dt.Rows.Add(id, GenerateReport(id, name, country));
    }

    SendEmail("Unpaid invoices", "Refer attached invoices", "test@gmail.com", dt);
}

private void SendEmail(string subect, string body, string to, DataTable data)
{
    using (MailMessage mailMessage = new MailMessage())
    {
        mailMessage.From = new MailAddress("test1@gmail.com");
        mailMessage.Subject = subect;
        mailMessage.Body = body;
        mailMessage.IsBodyHtml = true;
        mailMessage.To.Add(new MailAddress(to));
        foreach (DataRow dr in data.Rows)
        {
            Attachment attachment = new Attachment(new MemoryStream((byte[])dr["Data"]), dr["Id"].ToString() + ".pdf");
            mailMessage.Attachments.Add(attachment);
        }

        SmtpClient smtp = new SmtpClient();
        smtp.Host = "smtp.gmail.com";
        smtp.EnableSsl = true;
        System.Net.NetworkCredential NetworkCred = new System.Net.NetworkCredential();
        NetworkCred.UserName = mailMessage.From.Address;
        NetworkCred.Password = "password";
        smtp.UseDefaultCredentials = true;
        smtp.Credentials = NetworkCred;
        smtp.Port = 587;
        smtp.Send(mailMessage);
    }
}

private byte[] GenerateReport(string id, string name, string country)
{
    byte[] bytes = null;
    Document document = new Document(PageSize.A4, 88f, 88f, 100f, 10f);
    Font NormalFont = FontFactory.GetFont("Arial", 12, Font.NORMAL, Color.BLACK);
    using (MemoryStream memoryStream = new MemoryStream())
    {
        PdfWriter writer = PdfWriter.GetInstance(document, memoryStream);
        Phrase phrase = null;
        PdfPCell cell = null;
        PdfPTable table = null;
        document.Open();
        table = new PdfPTable(3);
        table.TotalWidth = 500f;
        table.LockedWidth = true;

        phrase = new Phrase();
        phrase.Add(new Chunk("Id", FontFactory.GetFont("Arial", 16, Font.BOLD, Color.RED)));
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT);
        table.AddCell(cell);

        phrase = new Phrase();
        phrase.Add(new Chunk("Name", FontFactory.GetFont("Arial", 16, Font.BOLD, Color.RED)));
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT);
        table.AddCell(cell);

        phrase = new Phrase();
        phrase.Add(new Chunk("Country", FontFactory.GetFont("Arial", 16, Font.BOLD, Color.RED)));
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT);
        table.AddCell(cell);

        phrase = new Phrase();
        phrase.Add(new Chunk(id, FontFactory.GetFont("Arial", 16, Font.NORMAL, Color.BLACK)));
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT);
        table.AddCell(cell);

        phrase = new Phrase();
        phrase.Add(new Chunk(name, FontFactory.GetFont("Arial", 16, Font.NORMAL, Color.BLACK)));
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT);
        table.AddCell(cell);

        phrase = new Phrase();
        phrase.Add(new Chunk(country, FontFactory.GetFont("Arial", 16, Font.NORMAL, Color.BLACK)));
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT);
        table.AddCell(cell);

        document.Add(table);
        document.Close();
        bytes = memoryStream.ToArray();
        memoryStream.Close();
    }

    return bytes;
}

private static PdfPCell PhraseCell(Phrase phrase, int align)
{
    PdfPCell cell = new PdfPCell(phrase);
    cell.BorderColor = Color.WHITE;
    cell.VerticalAlignment = PdfCell.ALIGN_TOP;
    cell.HorizontalAlignment = align;
    cell.PaddingBottom = 2f;
    cell.PaddingTop = 0f;
    return cell;
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As DataTable = New DataTable()
        dt.Columns.AddRange(New DataColumn(2) {
                            New DataColumn("Id"),
                            New DataColumn("Name"),
                            New DataColumn("Country")})
        dt.Rows.Add(1, "John Hammond", "United States")
        dt.Rows.Add(2, "Mudassar Khan", "India")
        dt.Rows.Add(3, "Suzanne Mathews", "France")
        dt.Rows.Add(4, "Robert Schidner", "Russia")
        GridView1.DataSource = dt
        GridView1.DataBind()
    End If
End Sub

Protected Sub OnSend(ByVal sender As Object, ByVal e As EventArgs)
    Dim dt As DataTable = New DataTable()
    dt.Columns.Add(New DataColumn("Id", GetType(String)))
    dt.Columns.Add(New DataColumn("Data", GetType(Byte())))

    For Each row As GridViewRow In GridView1.Rows
        Dim id As String = row.Cells(0).Text.Trim()
        Dim name As String = row.Cells(1).Text.Trim()
        Dim country As String = row.Cells(2).Text.Trim()
        dt.Rows.Add(id, GenerateReport(id, name, country))
    Next

    SendEmail("Unpaid invoices", "Refer attached invoices", "test@gmail.com", dt)
End Sub

Private Sub SendEmail(ByVal subect As String, ByVal body As String, ByVal [to] As String, ByVal data As DataTable)
    Using mailMessage As MailMessage = New MailMessage()
        mailMessage.From = New MailAddress("test1@gmail.com")
        mailMessage.Subject = subect
        mailMessage.Body = body
        mailMessage.IsBodyHtml = True
        mailMessage.To.Add(New MailAddress([to]))
        For Each dr As DataRow In data.Rows
            Dim attachment As Attachment = New Attachment(New MemoryStream(CType(dr("Data"), Byte())), dr("Id").ToString() & ".pdf")
            mailMessage.Attachments.Add(attachment)
        Next

        Dim smtp As SmtpClient = New SmtpClient()
        smtp.Host = "smtp.gmail.com"
        smtp.EnableSsl = True
        Dim NetworkCred As Net.NetworkCredential = New Net.NetworkCredential()
        NetworkCred.UserName = mailMessage.From.Address
        NetworkCred.Password = "password"
        smtp.UseDefaultCredentials = True
        smtp.Credentials = NetworkCred
        smtp.Port = 587
        smtp.Send(mailMessage)
    End Using
End Sub

Private Function GenerateReport(ByVal id As String, ByVal name As String, ByVal country As String) As Byte()
    Dim bytes As Byte() = Nothing
    Dim document As Document = New Document(PageSize.A4, 88.0F, 88.0F, 100.0F, 10.0F)
    Dim NormalFont As Font = FontFactory.GetFont("Arial", 12, Font.NORMAL, Color.BLACK)

    Using memoryStream As MemoryStream = New MemoryStream()
        Dim writer As PdfWriter = PdfWriter.GetInstance(document, memoryStream)
        Dim phrase As Phrase = Nothing
        Dim cell As PdfPCell = Nothing
        Dim table As PdfPTable = Nothing
        document.Open()
        table = New PdfPTable(3)
        table.TotalWidth = 500.0F
        table.LockedWidth = True
        phrase = New Phrase()
        phrase.Add(New Chunk("Id", FontFactory.GetFont("Arial", 16, Font.BOLD, Color.RED)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        table.AddCell(cell)
        phrase = New Phrase()
        phrase.Add(New Chunk("Name", FontFactory.GetFont("Arial", 16, Font.BOLD, Color.RED)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        table.AddCell(cell)
        phrase = New Phrase()
        phrase.Add(New Chunk("Country", FontFactory.GetFont("Arial", 16, Font.BOLD, Color.RED)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        table.AddCell(cell)
        phrase = New Phrase()
        phrase.Add(New Chunk(id, FontFactory.GetFont("Arial", 16, Font.NORMAL, Color.BLACK)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        table.AddCell(cell)
        phrase = New Phrase()
        phrase.Add(New Chunk(name, FontFactory.GetFont("Arial", 16, Font.NORMAL, Color.BLACK)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        table.AddCell(cell)
        phrase = New Phrase()
        phrase.Add(New Chunk(country, FontFactory.GetFont("Arial", 16, Font.NORMAL, Color.BLACK)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        table.AddCell(cell)
        document.Add(table)
        document.Close()
        bytes = memoryStream.ToArray()
        memoryStream.Close()
    End Using

    Return bytes
End Function

Private Shared Function PhraseCell(ByVal phrase As Phrase, ByVal align As Integer) As PdfPCell
    Dim cell As PdfPCell = New PdfPCell(phrase)
    cell.BorderColor = Color.WHITE
    cell.VerticalAlignment = PdfCell.ALIGN_TOP
    cell.HorizontalAlignment = align
    cell.PaddingBottom = 2.0F
    cell.PaddingTop = 0F
    Return cell
End Function

For more details on PDF generation refer below article.

How to generate and download PDF Report from database in ASP.Net using iTextSharp C# and VB.Net