Most failed redactions look perfect. A black rectangle over a name hides it on screen and in print, and leaves the name sitting in the file where anyone can select it, copy it, or search for it.
Open it, select across the redacted area, and copy. If text appears in your clipboard, it was only covered. For scans, extract the images from the file and look at them.
It should not. PalPDF removes only what sits under a cover — a word half covered loses the covered half and the rest stays exactly where it was.