How do I uninstall Neat Office? I accidentally selected it

On the Windows Start page, begin typing "control panel". Within a few characters, "Control Panel" will appear at the top of the list, so click it. In the Control Panel, click "Programs and Features". In the list of installed programs, locate and right-click on Neat Office and then click the "Uninstall/Change" popup. When prompted, enter the administrator password.

Usually at this point you'll see the beginning of the uninstaller, and you can just follow the prompts to do the job. If you get some kind of error, such as a missing file, you may want to get a copy of Revo Uninstaller Freeware from https://www.revouninstaller.com/revo-uninstaller-free-download/ .

Even if you can't get rid of Neat Office, you can still go to Windows Start > Settings > Apps > Default Apps > "Set defaults by app" and tell Windows to use the Microsoft Office programs as the defaults for their registered document types.

A "Quick Repair" of Microsoft Office will usually fix the file associations as well.

Repair an Office application - Office Support