I've created for my company a webapp that let company clients make queries against a database and get the output as a table. At this point they can export and download on own pc this table in .csv or .xlsx (the export is made by javascript code).
My company wants to prevent malicious clients reselling this files so I wanted to know if it's possible insert into these files an invisible identifier (as a metatag) to recoignize them to aim counteract industrial espionage or similar violations over this files.