public void GenerateDocument()
        {
            WordTemplate wt = new WordTemplate();
            wt.Open(@"..\..\WordTemplateFiles\NestedMailMergeTemplate.docx");
            //Retrieve the Data from the source, a csv file with a helper method
            DataTable dt = GetMailMergeData(@"..\..\WordData\NestedMailMergeData.csv");
          
            // set dt as the datasource for the repeatblock and "MailMerge" as the bookmark. 
            // this will cause wordwriter to bind each letter on a different page of the output file.
            wt.SetRepeatBlock(dt, "MailMerge");
            wt.Process();
            //Save the Document in the desired location
            wt.Save(@"..\..\WordOutputFiles\NestedMailMerge_output.docx");
        }

 Template: NestedMailMergeTemplate.docx

Output:  NestedMailMerge_output.docx