Correcting professors' lecture notes
I can only speak for myself, and I'm just a postdoc.

I would be indifferent if someone pointed out one or two typos; on the one hand that's helpful, on the other a bit pedantic.

However, if I received a "Word doc containing all the typos and mistakes [you] could find" in a 90 page document, I would be delighted and grateful.

As an aside, I'm currently working through a textbook to brush up my statistics skills. I'm trying to collect the mistakes that I stumble upon in order to send them to the author once I've finished the book, so he can correct them in the next edition.