Mail merge to a 40 pages MS word document using sharepoint 2013 and visual web part form

There is a 40 page word document to be used as a template and it has fields like name, age, address, site, numbers etc, across all the pages. The source of these fields come from sharepoint list which is using a input form in sharepoint 2013. The form is created using visual web part. It is required to replace text in word document once the user submits field values in SharePoint site using the available form. The new word document created can be stored at SharePoint library or local folder.