[if_by_whisky]

Guessing is actually easy. For the kinds of files that end up as redacted pdfs (legal, government, etc), there's probably 5-8 font options that make up 98% of documents. Sizes and weights are immediately recognizable to the slightly trained eye. I'm pretty sure I could guess all 3 attributes at a glance.

[happyopossum]

Or just look at the unredacted text around it and use that. Nobody is changing fonts on text before pixelation.