[Lawtan]

The hides (skin - treated so as to prevent protein decay and all) tend to come from farms nowadays, sometimes from hunters...so largely cattle and deer. It's use in the book industry was possibly where the idea of writing made flesh comes from.

I had to look up the human skin one. (Bad horror enthusiast - I should have already known xD). It has been done - enough to coin the term "Anthropodermic Bibliopegy" for books bound in human skin. I don't think the material would be as strong, though I think all vellum (book leather) lasts longer than paper.
Also, it was apparently a fad to use alongside cadaver study in the 17/18th centuries. Some folk have made themselves into books/keepsakes after they died.
Now, a company claiming to use donated human skin (it is an organ...so organ donation) sells leather at $14000 a wallet. Personally think that is more of a scam.

And yeah, essentially. Paper is processed plant tissue. Vellum processed animal tissue.

Interestingly, Vellum is better at preserving mistakes - when a record was "erased" and all. Sort of acts like a clay mold of the thing, and has been useful in finding old stories people tried to scrape away.