I've already posted this in the PDF24 Reader forum, but I see only 2 posts within the las 2 years. I'm wondering whether anyone is "watching" questions in that forum. So, I hope it's OK for me to also post it here. Here is that posting:
In the redact tool I don't see any button or arrow to select the area that I want to blacken.
I copy-pasted the link from my post in the PDF24 forum. Let's see if it works if I simply re-create the link here.
I wonder whether one of the icons outlined in green might be to identify the area to redact.