If I upgrade to Catalina from Mojave, will microsoft word for mac 2008 12.3 work on os 15.5?

Karen,

Your documents created in Office 2008 for Mac are unaffected by Catalina, only the application's themselves are inoperable. Just a heads up — Microsoft plans to retire Office 2016 for Mac this (2020) Fall, so a strategic purchase would be Office 365 (subscription, apps in Mac App Store), or the single-purchase Office 2019 for Mac. You will need to have a current, functional MS Office suite on Catalina before you can open the prior Word, etc documents in native document mode.

You could open/edit/save them in the free, 64-bit LIbreOffice Suite, which is a clone of MS Office — until ready to make a product decision in the first paragraph.

No. You will need Office for Mac 2016 or later to work on Catalina.

See the following for other options:

If you have an early version of Office for Mac 2016, you can update it at no charge. 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

No. This is a 32-bit application. Microsoft was informed by Apple years ago that soon, 32-bit apps will not be supported.

https://roaringapps.com/app/microsoft-office-2008

It’s time for you to upgrade.

All your Office documents will open with an app that opens Office documents. The 64 bit restriction applied to apps not documents.

karenfromcanyon wrote:

Will I have to buy the other program before I can open and continue to work on my word docs?

Yes ... concurrent with upgrading to MacOS Catalina.