> but developed to be [...] integrated in another product that handles documents, for example a file sharing solution, an online wiki, a project management tool and so on

It looks like it only provides the document editing part and you need an app around it to actually open the document from a filesystem and provide its content to this editing interface, and take the output and save it back to the filesystem? (Filesystem, or whatever persistent storage medium)

It's a WOPI app. Designed for embedding microsoft 365 office app in other web apps, but other people implement it. There's callabria, and this.

You'd use it to connect nextcloud to one of these providers. Probably some other enterprise apps I don't know about can use it to edit documents.