I had trouble with Word and deleted it. Can't open Word documents. Need to find a replacement.

The current version of Microsoft Word works well on a Mac running Catalina.

If you have an early version of Office for Mac 2016, you can update it at no charge. However note that connecting to Microsoft 365 services using Office 2016 for Mac is not supported by Microsoft after October 13, 2020. See: https://docs.microsoft.com/en-us/office365/troubleshoot/administration/office-2016-for-mac-64-bit-upgrade

If you have Office for Mac 2011 or earlier, you can either subscribe to Microsoft 365 or you can make a one-time purchase. See: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac?ms.officeurl=mac-compare-redir

Or use the free Microsoft Office on the web: https://products.office.com/en-us/free-office-online-for-the-web

Or Google Docs: https://www.google.com/docs/about/

Other options include using the free and very good Libre Office https://www.libreoffice.org/

or Apple's Pages and Numbers

An additional thought. As noted, there are some excellent alternatives. They can open Word files and can save as Word files. Be aware that when using an alternative program, some of the commands you may be used to using will be changed and some of the formatting of a file may be different. Otherwise, they work just as well.

Apple's applications perform document translations in opening, and the export of Office documents. Apple makes no promises as to the efficacy of this process, and the resulting documents may not appear as they once did in Microsoft applications.

For document fidelity, Microsoft's applications open their own documents in native mode without translation. The best document compatibility without MS Office installed would then be found in LibreOffice v7.

Apple's suite of apps are perfectly capable of handling Office files. Pages, Numbers, Keynote can all read/write Office documents and they are already on your Mac.