Ensuring that all those objects have been properly redacted, and none leaks anything that could cause trouble, is an almost impossible task. Not only that, but they often contain objects from previous edits, some of which may still contain text which is invisible to the user.
A typical PDF document consists of dozens or even thousands of objects containing snippets of text, each normally compressed and assembled in a complex tree. The PDF format was never designed for tasks such as redaction of content. This article looks at how thorough that is, and whether you can rely on it removing all access to sensitive content in your PDFs. I hadn’t noticed it before Big Sur, but Apple’s bundled Preview app can now redact PDF documents.
