editing PDF to add page number | VB.net - vb.net

Question

I am looking to modify the pdf to add the page number and I cannot find why the variable "cb" is empty.
you can see error on the screen below
Error on the screen : "Object reference not set to an instance of an object"

Answer 1

I just found how to edit pdf and add pages number, here is my code for those who need it.
I copy a file, I count the number of pages, in a while loop I display the number of pages (1/3) then I import the page on which I wanted to add the number of pages.
Public Sub ModifPDF(ByVal annee As Integer, ByVal mois As Integer, ByVal nomFichier As String, ByVal sourceFileList As String)
Dim Col1 As PdfPCell
Dim Col2 As PdfPCell
Dim Font1 As New Font(FontFactory.GetFont(FontFactory.HELVETICA, 1, iTextSharp.text.Font.NORMAL))
Dim Font8 As New Font(FontFactory.GetFont(FontFactory.HELVETICA, 8, iTextSharp.text.Font.NORMAL))
Dim Vide As PdfPCell = New PdfPCell(New Phrase("")) With {
.Border = 0
}
Dim reader As New PdfReader(sourceFileList)
Dim sourceFilePageCount As Integer = reader.NumberOfPages
Dim doc As New Document(reader.GetPageSizeWithRotation(1))
My.Computer.FileSystem.CopyFile(sourceFileList, "C:\test")
Dim writer As PdfWriter = PdfWriter.GetInstance(doc, New FileStream("C:\test", FileMode.Open, FileAccess.Write))
doc.Open()
Dim contentByte As PdfContentByte = writer.DirectContent
Dim pageIndex As Integer = 0
While pageIndex < sourceFilePageCount
pageIndex = pageIndex + 1
doc.SetPageSize(reader.GetPageSize(pageIndex))
Dim TableNota As PdfPTable = New PdfPTable(2)
Dim widthsNota As Single() = New Single() {19.7F, 1.5F}
TableNota.WidthPercentage = 97
TableNota.SetWidths(widthsNota)
Col1 = New PdfPCell(New Phrase(" ", Font8)) With {
.Border = 0
}
TableNota.AddCell(Col1)
Col2 = New PdfPCell(New Phrase("page " & pageIndex & "/" & sourceFilePageCount & "", Font8)) With {
.Border = 0
}
TableNota.AddCell(Col2)
TableNota.AddCell(Vide)
doc.Add(TableNota)
Dim page = writer.GetImportedPage(reader, pageIndex)
Dim rotation = reader.GetPageRotation(pageIndex)
If rotation.Equals(90) Then
contentByte.AddTemplate(page, 0, -0.1F, 1.0F, 0, 0, reader.GetPageSizeWithRotation(pageIndex).Height)
Else
contentByte.AddTemplate(page, 1.0F, 0, 0, 1.0F, 0, 0)
End If
doc.NewPage()
End While
doc.Close()
End Sub