Using this code as provided in your documentation for a Word XML file I get a Get Null Object from xml file.Make sure the xml file correct.
I can open the file in MS Word and it displays correctly.
FileStream fs = new FileStream("C:\\Test\\test1.xml",FileMode.Open);
Text text = Pdf.CreateObjFromXml(fs, null) as Text;
Aspose.Pdf.Section sec = pdf.Sections.Add();
sec.Paragraphs.Add(text);