In 2019, lawyers representing PaulManafort filed a response to special counsel Robert Muellers claims that he violated his cooperation agreement by repeatedly lying to prosecutors. Specific sections of this response were redacted before it was released to the public due to the sensitive nature of some of the content. However, it quickly became apparent that anyone with Adobe Acrobat, or other PDF viewing tools, could easily copy and paste the text that still existed under the redaction blocks to another document to reveal the passages that had been redacted.”]
Source: https://informationsecuritybuzz.com/articles/redacting-pdfs-a-simple-task-with-lots-of-consequences/