Mass Conversion of doc to docx ext.

Mass Conversion of doc to docx ext.

So, I'm making a FULL PLUNGE to Zoho for my Desktop & Android Office Ste.  I really do like it's intuitiveness, and economy of space, as well as it's easy implementation with Google (ALL) Docs, and Drive.  However, I'm trying to find a shortcut where I can associate/convert all DOC extentions to DOCX extensions.  On my desktop, since there's no downloadable app (i.e. Writer) that Win10 can associate with, Win10 thinks it's supposed to use WordPad.  So, is there any way to tell Win10 to associate, not just DOCX, extensions with Zoho, but convert old DOC extensions as well?  BTW, I'd like to convert/associate all XLS to XLSX spreadsheets, and same for presentations.

Thanks,
GPL