An example of how not to remove personal data in documents. (We removed the name here.)
You can easily copy the blackened line, and paste it somewhere else with data that shouldn't be there.
If you want to avoid something like this, black out lines, print out the file, and scan it afterwards.
Thanks for the tip, there is now an article on it: https://infosec-handbook.eu/blog/libreoffice63-redaction/
This instance was shut down on March 31st, 2020.