We recommend running a local Office suite. If you're using Microsoft Windows, we suggest Microsoft Office as it has support from MDAG which prevents untrusted Word, PowerPoint and Excel files from accessing trusted resources. Application Guard opens untrusted files in an isolated Hyper-V-enabled container. On macOS iWork has App Sandbox.
For other platforms, consider below:
LibreOffice is a free and open-source office suite with extensive functionality.
OnlyOffice is a cloud-based free and open-source office suite with extensive functionality, including integration with Nextcloud.
CryptPad is a private-by-design alternative to popular office tools. All content on this web service is end-to-end encrypted and can be shared with other users easily.