can I back up to icloud my pc working files like word docs and excel spreadsheets

Hello Al218,

Thank you for using Apple Support Communities.

Yes, you can store pretty much anything with some size and storage limits. See this question from the following FAQ:

What types of files can I store in iCloud Drive?

You can store any type of file in iCloud Drive, as long as it's less than 15 GB in size and you don't exceed your iCloud storage limit. There's no restriction on file type, so you keep all of your work documents, school projects, presentations, and more up to date across all of your devices. Learn more about managing your iCloud Drive files.

iCloud Drive FAQ - Apple Support

Regards,
Jeff D.