how to retrieve Word documents on Mac updated to Big Sur

If you were using Office 2008/2011 and upgraded to Big Sur, then they are toast, as only 64-bit application are supported, and that would require a new Microsoft 365 subscription, or a single-purchase of Office 2019 for Mac — either of which offer 64-bit applications.

Your Office documents are unaffected by the 32/64-bit issue, and can handily be opened by the free 64-bit LibreOffice Suite, an MS Office clone.

Although Apple provides Pages, Numbers, and Keynote v10.3.5 (currently) for Big Sur, these are not clones of MS Office applications, and will have less document compatibility than does LibreOffice.

The current Adobe Acrobat Reader DC works fine on Big Sur. It has an Update menu in its Help menu too.