> I haven't seen any redaction system yet that protects against this.
The linked article suggests widening redacted areas more than needed with some randomization applied to the width. Strikes me that that wouldn't do much except add a few more possible solutions.
> If the redaction is a person's name
Of course, you can also take this further. Even if you can't recover names you can get meta information about how many parties are involved by recognizing different length redactions correspond to different entities. While same length redaction doesn't guarantee same entity it is a hint.
Yeah, the more robust protection is to widen to a constant. But in the general case that could require reflowing the pdf. But honestly single word redactions are really probably useless with cheap AI that can highly accurately fill in the gaps