Is this an adverb

Answer 1

It can be, when it modifies an adjective as in "I didn't think the water was this deep" where it is a non-specific reference to another non-specific modifier.

The word is otherwise a pronoun ("This is Sparta!") or an adjective ("This town isn't big enough for both of us.")

Answer 2

The word "this" can be a pronoun, an adjective, or an adverb.

As an adverb, it would modify an adjective or adverb: this late, this far, this long.