Issue on Mail Merge template

HI ,
We are evaluating the Aspose for document/content management system for our product (elexratio.com) . We are facing an issue on the Mail merge template. A template is merging value only if mail merge place holder is created through code. But we should have an option for end-user to update the template with placeholders, want to understand if this is supported by Product. User will update template as part of intital setup or udpate

//DocumentBuilder builder = new DocumentBuilder(doc1);
//foreach (var str in lists.placeholders)
//{                                             
       //    builder.InsertField(" MERGEFIELD " + str + " ");
       //    builder.InsertParagraph();
//}

@appuelex

Can you please share the source file, generated file, desired output file and used sample code with us that we may try on our end to help you further.