MS Word 64-bit

If you want an official answer, check with Microsoft.

Patched-to-the-last-update (technically, 15.25 and later) Microsoft Office 2016 will probably mostly work on Catalina.

Microsoft support expects you will be using Office 2021, Office 2019, or Office 365, for support and updates.

Alternatives to Office: LibreOffice can read and write most Office documents (including some that Office itself was having trouble with), and Apple iWork Pages, Numbers, and Keynote can read and write many Office documents, and there are other alternatives.

The number of bits is not relevant. Most likely, you need to purchase something from Microsoft, and you need to ask them.

Excerpted from Contact a third-party vendor - Apple Support:

• Find Microsoft products on Microsoft's website and the App Store.