Hey Prince,
Check the Document Template feature (https://docs.mendix.com/refguide/document-templates/) where you can manage your data on UI side and feed the template you need to build. After generate the document, just call the Download file activity to save the file locally.
Nevertheless, you can also check the different modules available in the marketplace.
Hope this helps!
Daniel
Hello Prince,
Create one entity and generalize with System.FileDocument.
Create UI and You will be able to upload your Template document here.
Create another entity and make association with File management entity.
Make another UI,You will select your template there.and if you want to change the value of selected template in Mendix then you can use XLS file and can utilize excel importer/data importer widget.