Class Libraries & REST APIs for the developers to manipulate & process Files from Word, Excel, PowerPoint, Visio, PDF, CAD & several other categories in Web, Desktop or Mobile apps. Develop & deploy on Windows, Linux, MacOS & Android platforms.... Please use [Workbook.CustomXmlParts.Add()] ( https://reference...XML Part by ID, you can use [Workbook.CustomXmlParts.SelectByID()]...