Open Office

I recommend that you download and install LIbreOffice, as it receives far better updates and frequency that OpenOffice. Because both are installed from outside of the Mac App Store, you will still need to provide the one-time verification process. Right-click on the LibreOffice icon in your /Applications folder, and choose Open. A verification panel will appear, and when it has completed, another dialog will appear informing you what you already know. Click the Open button on that dialog, and LibreOffice will launch.

Your existing OpenOffice documents are compatible with LibreOffice.

I read your experience and I was concerned about my use of libreoffice, it failed to start, but I downloaded the latest version and that worked. I would check for an OpenOffice update.