That’s the logical next step up from paper prototyping.
PowerPoint or other digitally-enabled prototyping is a step DOWN from paper prototyping, not up.
With a PowerPoint prototype, the polished look sends a blatant cue to the person evaluating the system: we have already designed this, we care, and if you tell us we screwed up, you will be hurting our feelings and making us do extra work.
With paper prototypes, you provide the opposite cues: this system is totally open to changes, it’s easy to change, nothing is set in stone, we aren’t married to the design, we welcome your input, you are part of the team, changing this is no big deal, it’s going to change anyway.
You can state all these things verbally, but the reality of a paper prototype states them at a much more visceral level and really removes the inhibitions, both conscious and unconscious.
Paper, post-it notes, sharpies, highlighters, pencils, erasers, index cards… these are way better tools than software tools.
Oh, and by the way, moving a post-it note from one side of a “screen” to another is WAY faster than doing it in PowerPoint. You can move two at once, float them around, try things out, undo instantly, set things aside, hand over control… The user/test subject can do it themselves without the social friction of having to say “um, would it be OK if I used your mouse to edit your document?” You could give them control of your computer, but still the difference in what they do is like night and day.