This statement provides insight into how hackers may have been able to access his system. On October 24, NextCloud disclosed a remote code execution vulnerability (CVE-2019-11043) which has been exploited to compromise servers with the default Nextcloud NGINX configuration.
Source: NextCry Ransomware Targets NextCloud Linux Servers and Remains Undetected Features
ownCloud Documents is collaborative editing of rich-text documents. The documents can be created from within the web-interface or existing documents can be uploaded. Sharing and editing can be done securely in the browser and be shared inside ownCloud or via a public link. User that have an account on the same server can be invited or public invitations can also be sent be email. The editing works on top of normal ODF files that are stored in ownCloud. ownCloud Documents is built in cooperation with KO GmbH
I haven’t tried this solution out yet.