Protect PDF file being converted to other format in ASP.Net using C# and VB.Net

Please refer below modified code.

 Code

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
        BindEmployeesDropDown()
    End If
End Sub

Private Sub BindEmployeesDropDown()
    ddlEmployees.DataSource = GetData("SELECT EmployeeId, (FirstName + ' ' + LastName) Name FROM Employees")
    ddlEmployees.DataTextField = "Name"
    ddlEmployees.DataValueField = "EmployeeId"
    ddlEmployees.DataBind()
End Sub

Private Function GetData(query As String) As DataTable
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Dim cmd As New SqlCommand(query)
    Using con As New SqlConnection(conString)
        Using sda As New SqlDataAdapter()
            cmd.Connection = con

            sda.SelectCommand = cmd
            Using dt As New DataTable()
                sda.Fill(dt)
                Return dt
            End Using
        End Using
    End Using
End Function

Protected Sub GenerateReport(sender As Object, e As EventArgs)
    Dim dr As DataRow = GetData("SELECT * FROM Employees where EmployeeId = " + ddlEmployees.SelectedItem.Value).Rows(0)
    Dim document As New Document(PageSize.A4, 88.0F, 88.0F, 10.0F, 10.0F)
    Dim NormalFont As Font = FontFactory.GetFont("Arial", 12, Font.NORMAL, Color.BLACK)
    Using MemoryStream As 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
        Dim color__1 As Color = Nothing

        document.Open()

        'Header Table
        table = New PdfPTable(2)
        table.TotalWidth = 500.0F
        table.LockedWidth = True
        table.SetWidths(New Single() {0.3F, 0.7F})

        'Company Logo
        cell = ImageCell("~/images/northwindlogo.gif", 30.0F, PdfPCell.ALIGN_CENTER)
        table.AddCell(cell)

        'Company Name and Address
        phrase = New Phrase()
        phrase.Add(New Chunk("Microsoft Northwind Traders Company" & vbLf & vbLf, FontFactory.GetFont("Arial", 16, Font.BOLD, Color.RED)))
        phrase.Add(New Chunk("107, Park site," & vbLf, FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)))
        phrase.Add(New Chunk("Salt Lake Road," & vbLf, FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)))
        phrase.Add(New Chunk("Seattle, USA", FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        cell.VerticalAlignment = PdfCell.ALIGN_TOP
        table.AddCell(cell)

        'Separater Line
        color__1 = New Color(System.Drawing.ColorTranslator.FromHtml("#A9A9A9"))
        DrawLine(writer, 25.0F, document.Top - 79.0F, document.PageSize.Width - 25.0F, document.Top - 79.0F, color__1)
        DrawLine(writer, 25.0F, document.Top - 80.0F, document.PageSize.Width - 25.0F, document.Top - 80.0F, color__1)
        document.Add(table)

        table = New PdfPTable(2)
        table.HorizontalAlignment = Element.ALIGN_LEFT
        table.SetWidths(New Single() {0.3F, 1.0F})
        table.SpacingBefore = 20.0F

        'Employee Details
        cell = PhraseCell(New Phrase("Employee Record", FontFactory.GetFont("Arial", 12, Font.UNDERLINE, Color.BLACK)), PdfPCell.ALIGN_CENTER)
        cell.Colspan = 2
        table.AddCell(cell)
        cell = PhraseCell(New Phrase(), PdfPCell.ALIGN_CENTER)
        cell.Colspan = 2
        cell.PaddingBottom = 30.0F
        table.AddCell(cell)

        'Photo
        cell = ImageCell(String.Format("~/photos/{0}.jpg", dr("EmployeeId")), 25.0F, PdfPCell.ALIGN_CENTER)
        table.AddCell(cell)

        'Name
        phrase = New Phrase()
        phrase.Add(New Chunk(dr("TitleOfCourtesy").ToString & " " + dr("FirstName").ToString & " " + dr("LastName").ToString, FontFactory.GetFont("Arial", 10, Font.BOLD, Color.BLACK)))
        phrase.Add(New Chunk("(" + dr("Title").ToString() + ")", FontFactory.GetFont("Arial", 8, Font.BOLD, Color.BLACK)))
        cell = PhraseCell(phrase, PdfPCell.ALIGN_LEFT)
        cell.VerticalAlignment = PdfPCell.ALIGN_MIDDLE
        table.AddCell(cell)
        document.Add(table)

        DrawLine(writer, 160.0F, 80.0F, 160.0F, 690.0F, Color.BLACK)
        DrawLine(writer, 115.0F, document.Top - 200.0F, document.PageSize.Width - 100.0F, document.Top - 200.0F, Color.BLACK)

        table = New PdfPTable(2)
        table.SetWidths(New Single() {0.5F, 2.0F})
        table.TotalWidth = 340.0F
        table.LockedWidth = True
        table.SpacingBefore = 20.0F
        table.HorizontalAlignment = Element.ALIGN_RIGHT

        'Employee Id
        table.AddCell(PhraseCell(New Phrase("Employee code:", FontFactory.GetFont("Arial", 8, Font.BOLD, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        table.AddCell(PhraseCell(New Phrase("000" + dr("EmployeeId"), FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        cell = PhraseCell(New Phrase(), PdfPCell.ALIGN_CENTER)
        cell.Colspan = 2
        cell.PaddingBottom = 10.0F
        table.AddCell(cell)


        'Address
        table.AddCell(PhraseCell(New Phrase("Address:", FontFactory.GetFont("Arial", 8, Font.BOLD, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        phrase = New Phrase(New Chunk(dr("Address").ToString, FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)))
        phrase.Add(New Chunk(dr("City").ToString + vbLf, FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)))
        phrase.Add(New Chunk(dr("Region").ToString + " " + dr("Country").ToString + " " + dr("PostalCode").ToString, FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)))
        table.AddCell(PhraseCell(phrase, PdfPCell.ALIGN_LEFT))
        cell = PhraseCell(New Phrase(), PdfPCell.ALIGN_CENTER)
        cell.Colspan = 2
        cell.PaddingBottom = 10.0F
        table.AddCell(cell)

        'Date of Birth
        table.AddCell(PhraseCell(New Phrase("Date of Birth:", FontFactory.GetFont("Arial", 8, Font.BOLD, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        table.AddCell(PhraseCell(New Phrase(Convert.ToDateTime(dr("BirthDate")).ToString("dd MMMM, yyyy"), FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        cell = PhraseCell(New Phrase(), PdfPCell.ALIGN_CENTER)
        cell.Colspan = 2
        cell.PaddingBottom = 10.0F
        table.AddCell(cell)

        'Phone
        table.AddCell(PhraseCell(New Phrase("Phone Number:", FontFactory.GetFont("Arial", 8, Font.BOLD, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        table.AddCell(PhraseCell(New Phrase(dr("HomePhone") + " Ext: " + dr("Extension"), FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        cell = PhraseCell(New Phrase(), PdfPCell.ALIGN_CENTER)
        cell.Colspan = 2
        cell.PaddingBottom = 10.0F
        table.AddCell(cell)

        'Addtional Information
        table.AddCell(PhraseCell(New Phrase("Addtional Information:", FontFactory.GetFont("Arial", 8, Font.BOLD, Color.BLACK)), PdfPCell.ALIGN_LEFT))
        table.AddCell(PhraseCell(New Phrase(dr("Notes").ToString(), FontFactory.GetFont("Arial", 8, Font.NORMAL, Color.BLACK)), PdfPCell.ALIGN_JUSTIFIED))
        document.Add(table)
        document.Close()
        Dim bytes As Byte() = MemoryStream.ToArray()
        MemoryStream.Close()

        Using input As New MemoryStream(bytes)
            Using output As New MemoryStream()
                Dim password As String = ddlEmployees.SelectedItem.Value & dr("FirstName") 'Set dynamic password as per your logic.
                Dim reader As New PdfReader(input)
                PdfEncryptor.Encrypt(reader, output, True, password, password, PdfWriter.ALLOW_SCREENREADERS)
                bytes = output.ToArray()
            End Using
        End Using
        Response.Clear()
        Response.Buffer = True
        Response.ContentType = "application/pdf"
        Response.AddHeader("Content-Disposition", "attachment; filename=Employee.pdf")
        Response.Cache.SetCacheability(HttpCacheability.NoCache)
        Response.BinaryWrite(bytes)
        Response.End()
        Response.Close()
    End Using
End Sub

Private Sub CriaRelatorioPDF(ByVal pCPF As String, ByVal pDados As String, ByVal pEmenta As String, ByVal pDataEmissao As String, ByVal pImgAssPresidente As String,
                        ByVal pImgAssCoordenador As String, ByVal pAssPresidente As String, ByVal pAssCoordenador As String, ByVal pSenha As String)

    Dim pCaminho As String
    pCaminho = Server.MapPath("pdfs")

    If File.Exists(pCaminho + "/" & pCPF & ".pdf") Then
        File.Delete(pCaminho + "/" & pCPF & ".pdf")
    End If

    'Atribuir fontes do servidor na aplicação
    FontFactory.RegisterDirectory("C:\WINDOWS\Fonts")
    Dim cellFont As Font = FontFactory.GetFont("Soleto-Light", 16.0F, Font.NORMAL)
    Dim cellFont3 As Font = FontFactory.GetFont("Soleto-Light", 9.0F, 0, Color.BLACK)

    'Criar uma instância de document
    Dim doc As New Document(iTextSharp.text.PageSize.A4.Rotate, 20, 20, 20, 20)
    PdfWriter.GetInstance(doc, New FileStream(pCaminho + "/" & pCPF & ".pdf", FileMode.Create))
    hfArquivo.Value = "pdfs/" & pCPF & ".pdf"

    Dim phraseDados As Phrase = Nothing 'Texto
    Dim phraseAss1 As Phrase = Nothing 'Frase da Assinatura 1
    Dim cellAss1 As PdfPCell = Nothing 'Célula da assinatura 1
    Dim cellImg1 As PdfPCell = Nothing 'Célula da imagem da assinatura 1

    Dim phraseAss2 As Phrase = Nothing 'Frase da Assinatura 2
    Dim cellAss2 As PdfPCell = Nothing 'Célula da assinatura 2
    Dim cellImg2 As PdfPCell = Nothing 'Célula da imagem da assinatura 2

    'Criar tabela ====================================================================
    Dim table1 As PdfPTable = New PdfPTable(New Single() {10, 80, 10})
    table1.DefaultCell.HorizontalAlignment = Element.ALIGN_JUSTIFIED 'Justificar texto
    table1.SpacingBefore = 220.0F 'Definir altura onde a tabela será criada
    table1.DefaultCell.BorderWidth = 0 'Largura da borda da tabela 1
    table1.DefaultCell.FixedHeight = 50.0F 'Altura da tabela 1
    table1.AddCell(" ") 'Coluna 1, Linha 1

    Dim htmlarraylist As ArrayList = HTMLWorker.ParseToList(New StringReader(pDados), Nothing)
    phraseDados = New Phrase()
    For k As Integer = 0 To htmlarraylist.Count - 1
        phraseDados.Add(CType(htmlarraylist(k), IElement))
    Next

    table1.AddCell(phraseDados) 'Coluna 2, Linha 1
    table1.AddCell(" ") 'Coluna 3, Linha 1

    Dim table2 As PdfPTable = New PdfPTable(New Single() {10, 80, 10})
    table2.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER 'Centralizar
    table2.DefaultCell.BorderWidth = 0 'Largura da borda da tabela 2
    table2.DefaultCell.FixedHeight = 50.0F 'Altura da tabela 2
    table2.AddCell(" ") 'Coluna 1, Linha 1
    table2.AddCell(pDataEmissao) 'Coluna 2, Linha 1
    table2.AddCell(" ") 'Coluna 3, Linha 1

    Dim table3 As PdfPTable = New PdfPTable(New Single() {10, 30, 10, 30, 10})
    phraseAss1 = New Phrase()
    phraseAss1.Add(New Chunk(pAssPresidente & vbLf & "Diretor Presidente", FontFactory.GetFont("Soleto-Light", 9, Font.NORMAL, Color.BLACK)))

    phraseAss2 = New Phrase()
    phraseAss2.Add(New Chunk(pAssCoordenador & vbLf & "Coordenador(a)", FontFactory.GetFont("Soleto-Light", 9, Font.NORMAL, Color.BLACK)))

    table3.SpacingBefore = 60.0F 'Definir altura onde a tabela será criada

    table3.DefaultCell.HorizontalAlignment = Element.ALIGN_CENTER 'Centralizar texto
    table3.DefaultCell.BorderWidth = 0 'Largura da borda da tabela

    table3.AddCell("") 'Coluna 1, Linha 1
    table3.AddCell("") 'Coluna 2, Linha 1
    table3.AddCell(" ") 'Coluna 3, Linha 1
    table3.AddCell(" ") 'Coluna 4, Linha 1
    table3.AddCell(" ") 'Coluna 5, Linha 1

    table3.AddCell("") 'Coluna 1, Linha 1
    table3.AddCell("_______________________________") 'Coluna 2, Linha 1
    table3.AddCell(" ") 'Coluna 3, Linha 1
    table3.AddCell("_______________________________") 'Coluna 4, Linha 1
    table3.AddCell(" ") 'Coluna 5, Linha 1

    table3.AddCell(" ") 'Coluna 1, Linha 2
    table3.AddCell(phraseAss1) 'Coluna 2, Linha 2
    table3.AddCell(" ") 'Coluna 3, Linha 2
    table3.AddCell(phraseAss2) 'Coluna 4, Linha 2
    table3.AddCell(" ") 'Coluna 5, Linha 2
    table3.AddCell(" ") 'Coluna 1, Linha 2
    table3.AddCell("") 'Coluna 2, Linha 2
    table3.AddCell(" ") 'Coluna 3, Linha 2
    table3.AddCell("") 'Coluna 4, Linha 2
    table3.AddCell(" ") 'Coluna 5, Linha 2

    'Definindo a imagem de fundo do documento
    Dim imageFilePath As String = Server.MapPath("~/imagens/Cedula_Certificado_01.jpg")
    Dim jpg As iTextSharp.text.Image = iTextSharp.text.Image.GetInstance(imageFilePath)
    jpg.ScaleToFit(850, 650)
    jpg.Alignment = iTextSharp.text.Image.UNDERLYING
    jpg.SetAbsolutePosition(0, 0)

    'Definindo imagem da assinatura 1
    Dim imageFilePath2 As String = pImgAssPresidente 'Server.MapPath("~/imagens/Cedula_Certificado_01.jpg")
    Dim jpgAssina1 As iTextSharp.text.Image = iTextSharp.text.Image.GetInstance(imageFilePath2)
    jpgAssina1.ScalePercent(10.0F)
    jpgAssina1.Alignment = iTextSharp.text.Image.UNDERLYING
    jpgAssina1.SetAbsolutePosition(155, 100)

    'Definindo imagem da assinatura 2
    Dim imageFilePath3 As String = pImgAssCoordenador 'Server.MapPath("~/imagens/Cedula_Certificado_01.jpg")
    Dim jpgAssina2 As iTextSharp.text.Image = iTextSharp.text.Image.GetInstance(imageFilePath3)
    jpgAssina2.ScalePercent(10.0F)
    jpgAssina2.Alignment = iTextSharp.text.Image.UNDERLYING
    jpgAssina2.SetAbsolutePosition(440, 100)

    '=================================================================================

    doc.Open()

    doc.Add(jpg)
    doc.Add(jpgAssina1) 'Assinatura do Presidente
    doc.Add(jpgAssina2) 'Assinatura do Coordenador

    doc.Add(New Paragraph(" "))
    doc.Add(table1)

    doc.Add(New Paragraph(" "))
    doc.Add(table2)

    doc.Add(table3)

    ' ######################################################################################
    'THIS PAGE DOES NOT CREATE
    ' ######################################################################################
    doc.NewPage()

    Dim html As ArrayList = HTMLWorker.ParseToList(New StringReader(pEmenta), Nothing)
    For k As Integer = 0 To html.Count - 1
        doc.Add(CType(html(k), IElement))
    Next
    doc.Close()

    If File.Exists(pCaminho + "/" & pCPF & ".pdf") Then
        hlDownload.NavigateUrl = "~/aluno/pdfs/" & pCPF & ".pdf"
        hlDownload.Visible = True
    End If

    ' =================================================================================

    ' #####################################################################################
    ' CREATE PASSWORD ON DOCUMENT
    ' #####################################################################################

    Dim bytes As Byte() = File.ReadAllBytes(pCaminho + "/" & pCPF & ".pdf")
    Using input As New MemoryStream(bytes)
        Using output As New MemoryStream()
            Dim password As String = ""
            Dim reader As New PdfReader(input)
            PdfEncryptor.Encrypt(reader, output, True, password, password, PdfWriter.ALLOW_SCREENREADERS)
            bytes = output.ToArray()
        End Using
    End Using
    ' #####################################################################################

    Response.Buffer = True
    Response.ContentType = "application/pdf"
    Response.AddHeader("content-disposition", "attachment;filename=Employee.pdf")
    Response.Cache.SetCacheability(HttpCacheability.NoCache)
    Response.BinaryWrite(bytes)
    Response.End()
    Response.Close()
End Sub

Private Shared Sub DrawLine(writer As PdfWriter, x1 As Single, y1 As Single, x2 As Single, y2 As Single, color As Color)
    Dim contentByte As PdfContentByte = writer.DirectContent
    contentByte.SetColorStroke(color)
    contentByte.MoveTo(x1, y1)
    contentByte.LineTo(x2, y2)
    contentByte.Stroke()
End Sub

Private Shared Function PhraseCell(phrase As Phrase, align As Integer) As PdfPCell
    Dim cell As New PdfPCell(phrase)
    cell.BorderColor = Color.WHITE
    cell.VerticalAlignment = PdfCell.ALIGN_TOP
    cell.HorizontalAlignment = align
    cell.PaddingBottom = 2.0F
    cell.PaddingTop = 0.0F
    Return cell
End Function

Private Shared Function ImageCell(path As String, scale As Single, align As Integer) As PdfPCell
    Dim image As iTextSharp.text.Image = iTextSharp.text.Image.GetInstance(HttpContext.Current.Server.MapPath(path))
    image.ScalePercent(scale)
    Dim cell As New PdfPCell(image)
    cell.BorderColor = Color.WHITE
    cell.VerticalAlignment = PdfCell.ALIGN_TOP
    cell.HorizontalAlignment = align
    cell.PaddingBottom = 0.0F
    cell.PaddingTop = 0.0F
    Return cell
End Function