This. I had no idea what this did until I read a couple of HN-comments. The short introduction could mean a couple of things:

Just downgrading the pdf? Looking for a signature-like part and turns this to pseduo-handwritten characters, maybe changing the color? Something completely different?

Naturally, I did not want to upload a potentially confidential document to some random webservice.

I actually had a pdf file containing several pages of "Lorem ipsum" that I needed for another thing, but I deleted it yesterday because I was done with it.