If an app on your iPhone or iPad stops responding, closes unexpectedly or won’t open, Apple offers the following guidance:
Close and reopen the app
Force the app to close. Then open the app to see if it's working as expected.
Restart your device
Restart your iPhone or restart your iPad. Then open the app to see if it's working as expected.
Check for updates
To see if updates are available for the app, open the App Store, tap your profile icon, then tap App Updates. If updates aren’t available for the app, update the software on your iPhone or iPad.
Delete the app, then re-download it
Delete the app. When you do this, you may lose data that was stored in the app. Then re-download the app. Then check whether the problem with the app is fixed.
The associated Apple Support page can be found here,
If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support
For Word and other Microsoft Apps, should you require technical assistance, you would be best advised to seek assistance from Microsoft's online help and support resources - as they are best placed to offer product and troubleshooting guidance for their Apps.
https://support.microsoft.com/en-us/word/word-for-ipad-help