It copies the data from the primary.
No. Nothing but Elasticsearch may change Elasticsearch's data. Quoting the same docs as last time:
WARNING : Don’t modify anything within the data directory or run processes that might interfere with its contents. If something other than Elasticsearch modifies the contents of the data directory, then Elasticsearch may fail, reporting corruption or other data inconsistencies, or may appear to work correctly having silently lost some of your data.