No there is no information passing through if the opacity is 100%. I have seen people attempting to redact using the pen or paintbrush tool, however, and opacit

No there is no information passing through if the opacity is 100%. I have seen people attempting to redact using the pen or paintbrush tool, however, and opacity is often not 100% when doing that. I have also seen people try to redact by drawing a black block on a new layer in Photoshop, for example, and then exporting as PDF. They're unaware that the layers are being exported in the PDF and the block can be removed. Always flatten your document completely before export.