I can test that for you (on a non-sensitive pdf of course). Only when you modify the underlying PostScript code in the PDF is it really redacted by software. Acrobat Professional and Adobe Illustrator can for sure.
If you print it and use ink and rescan it …I’d trust that too,
I speak as the graphic dept’s computer guy for one of those investment joints 27 years, after a stint at an ad agency. Nothing tests like …a test!