Mike and Chris have suggested using the Excel Import and Excel Exporter modules from the Mendix Marketplace. I think this is probably the best approach, and the one I would take.
If you are comfortable with Java, then you could look at creating your own Java Action using the Apache POI library. This is designed for handling Microsoft documents from Java, and it's what the Excel Importer and Exporter use themselves.
It depends on your needs. It would be easier to support an app that uses Excel Importer and Excel Exporter in the long term.
I am not 100% sure if this will fit your needs, but you could use both the Excel Importer module (to import and Excel file into Mendix), then manipulate the data as needed and use the Excel Exporter module to create and download a new Excel file.
Yes. You can use the Excel Import module to read the data into Mendix from an existing spreadsheet.
https://marketplace.mendix.com/link/component/72
Manipulate the data in Mendix as needed and export to new Excel file via Excel Export module.
https://marketplace.mendix.com/link/component/726