From Microsoft:

Support for Windows 8 ended on January 12, 2016, and support for Windows 8.1 will end on January 10, 2023.

Microsoft 365 Apps is no longer supported on Windows 8 or Windows 8.1 after they have reached their end of support dates. To avoid performance and reliability issues, we recommend that you move to a newer version of Windows.

A lot of software was not able to be used after Win10 was released, so you'd best keep the Win8 you're using running until you can find a new program to load to and convert your files.