In that case, you don't need iTextSharp. Create a generic handler (.ashx file), retrieve the binary data from the database in the ProcessRequest Method and send it to the client.

Public Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest
    Dim pdfID As Integer = Convert.ToInt32(context.Request.QueryString("pdfID"))
    Using myConnection As New SqlConnection(ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString)


        Const SQL As String = "SELECT [pdfData] FROM [pdfTable] WHERE [pdfID] = @pdfID"
        Dim myCommand As New SqlCommand(SQL, myConnection)
        myCommand.Parameters.AddWithValue("@pdfID", pdfID)


        myConnection.Open()
        Dim myReader As SqlDataReader = myCommand.ExecuteReader


        If myReader.Read Then
          context.Response.ContentType = "application/pdf"
          context.Response.BinaryWrite(myReader("pdfData"))
          context.Response.AddHeader("Content-Disposition", "attachment; filename=download.pdf"
        End If


        myReader.Close()
        myConnection.Close()
    End Using
End Sub

 To retrieve the pdf, call the ashx file like:

<asp:HyperLink ID="HyperLink1" runat="server" navigetUrl="~/pdf.ashx?pdfID=1" Text="Download" />