My computer says the Catalina update was successful but I still am not able to get into the office app.

If you have a Microsoft 365 subscription, you can download the apps from the Mac App Store for Word, Excel, Outlook, and Powerpoint and sign into them with your Microsoft account.

If not, you will need to purchase the standalone version of Office 2019 from Microsoft.

If you already own it, follow Microsoft's instructions on how to install it.

Your Microsoft Office documents are fine.

You're likely using an ancient and unsupported version of Microsoft Office; Office 2011 or earlier.

Older and unsupported versions of Office are 32-bit apps, and weren’t updated to the current 64-bit requirements.

You will need to purchase Microsoft Office 2019 apps, or purchase an Office 365 subscription, or migrate to and use the free LibreOffice app, or use the Apple iWork apps Pages, Numbers, and Keynote (free in the App Store) and which can read and write many Office documents.

Microsoft Office 2016 and later will work. Office 2011 and earlier will not work. Office 2019 and Office 365 subscriptions are the current Microsoft offerings.

Applecomputerapphelp wrote:

I have deleted the Microsoft application from my iMac. How to I reinstate the office system on my computer?

You will need to purchase Microsoft Office 2019 apps, or purchase an Office 365 subscription, or migrate to and use the free LibreOffice app, or use the Apple iWork apps Pages, Numbers, and Keynote (free in the App Store) and which can read and write many Office documents.

You buy and download Office from Microsoft.