Replace Text with iTextSharp7

Dim reader = New PdfReader(fileSrc)
Using pdfDoc = New PdfDocument(reader, New PdfWriter(fileDest))
    Dim n = pdfDoc.GetNumberOfPages()
    For i = 1 To n
        Dim page = pdfDoc.GetPage(i)
        Dim dict = page.GetPdfObject()
        Dim contents = dict.GetAsStream(PdfName.Contents)
        Dim bytes = reader.ReadStreamBytes(contents, True)
        Dim contentsDecoded = Encoding.UTF8.GetString(bytes)

        contentsDecoded = contentsDecoded.Replace("ReplaceThis", "WithThis")
        contents.SetData(Encoding.UTF8.GetBytes(contentsDecoded))
    Next
End Using