Spire.Doc 11.8.9 では数学式を OfficeMathMLCode に変換する機能が追加されました

    Document doc = new Document();
            doc.LoadFromFile("1.docx");
            StringBuilder stringBuilder = new StringBuilder();

            foreach (Section section in doc.Sections)
            {
                foreach (Paragraph par in section.Body.Paragraphs)
                {
                    foreach (DocumentObject obj in par.ChildObjects)
                    {
                        OfficeMath omath = obj as OfficeMath;
                        if (omath == null) continue;
                        string mathml = omath.ToOfficeMathMLCode();
                        stringBuilder.Append(mathml);
                        stringBuilder.Append("\r\n");
                    }
                }
            }
            File.WriteAllText("1.txt", stringBuilder.ToString());
            doc.Close();

Document doc = new Document();
                doc.LoadFromFile("Test.docx");
                var fieldNames = new string[] { "MyImage" };
                var fieldValues = new string[] { "logo.png" };

                doc.MailMerge.MergeImageField += new MergeImageFieldEventHandler(MailMerge_MergeImageField);

                doc.MailMerge.Execute(fieldNames, fieldValues);

                doc.SaveToFile("result.docx", FileFormat.Docx);
            }

            void MailMerge_MergeImageField(object sender, MergeImageFieldEventArgs field)
            {
                string filePath = field.FieldValue as string;
                if (!string.IsNullOrEmpty(filePath))
                {
                    field.Image = Image.FromFile(filePath);
                    field.ImageLink = "https://www.e-iceblue.com/";
                }

            }