Hello @jimboo
First of all, please note that you are using quite outdated version of ONLYOFFICE Docs. I recommend updating to the actual version.
As for the query: information about usage of Download as button is written into the log of DocService in DEBUG level logging. Here is an example:
[2025-01-04T13:20:17.217] [DEBUG] [localhost] [key] [userId] nodeJS - Start downloadAs: {"c":"save","id":"key","userid":"userId","outputformat":65,"title":"Title.docx","nobase64":true,"isSaveAs":false,"saveAsPath":null,"lcid":9,"savetype":3,"saveindex":1,"userconnectionid":"userId"}
[2025-01-04T13:20:17.233] [DEBUG] [localhost] [key] [userId] nodeJS - End downloadAs: {"type":"save","status":"ok","data":"data"}
I believe the only option here us to implement a watcher for such records in logs of Document Server separately that will send specific data to your storage application.
To enable debug-level logging, you need to modify production.json config in /etc/onlyoffice/documentserver/log4js/ directory as such:
"level": "DEBUG"
And then restart services with supervisorctl restart all for Docker or systemctl restart ds-* for DEB/RPM packages installation types.