Fileformatconverters.exe Download Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint File Formats from Official Microsoft Download Center will allow older Office editions to open the docx and xlsx formats.
Although MS don't mention it, even Office 97 programs work with it! Note the compact toolbars that could not possibly work effectively with touch screens - but are absolutely brilliant with a mouse. Office 97 does a full or custom install in less than 5 minutes on Windows 8 or 10 compatible hardware, and the component applications are much snappier than their modern counterparts. When you print your documents, you can not tell which edition was used.
I think that In XP and possibly Windows 7, Excel and Powerpoint could use the functionality of the fileformatconverters to save and open recent formats directly from the file save and file open dialogs, but that functionality has been lost in Windows 8 and 10, but I may not be remembering correctly.