Document document = new Document();
document.LoadFromFile("in.docx");
Section section = document.Sections[0];
document.StartTrackRevisions("Spire", DateTime.Now);
Paragraph para = section.Paragraphs[0];
para.Text = "added";
document.StopTrackRevisions();
document.SaveToFile("result.docx", FileFormat.Docx2010);
document.Dispose();