I think you are missing the point. 

Yes if the client wants to pay me to do manual redactions I can do it. But I would rather not do it. It's tedious and doesn't generate much revenue, and we have a lot more important work. 

Client can't do it themselves because no way to scan the papers in after they black out the numbers. I guess they could go to Kinkos maybe, but aside from that there's nothing. 

it's usually the case that a client COULD do a task themselves, but this is an annoying way to dodge the question of why the feature the program has or should have either doesn't exist or doesn't work.