there is a cloud published on the Internet Owncloud
additionally installed ONLYOFFICE Document server to open word-, excel- documents in the browser.
Question: ONLYOFFICE Document server is enough to deploy in the Owncloud local area network or do I need to publish it also on the Internet?
As far as I know the ONLYOFFICE server also needs to be published as the document is being loaded as an iFrame inside ownCloud.
As eneubauer already wrote, the port 443 (or 80 respectively) must be open, so remote users can connect to the document server. A full list is provided in the onlyoffice docs: https://helpcenter.onlyoffice.com/de/server/docker/document/open-ports.aspx