Is the word this a demonstrative pronoun?

Yes, the Word 'this' functions as a demonstrative pronoun, a Word that takes the place of a noun indicating near or far in place or time.
The demonstrative pronouns are: this, that, these, those.
Example: "I want this!", said Midge pointing to her choice on the dessert cart.

The Word 'this' also functions as an adjective when placed befor a noun.

Example: "This cake is delicious!", said Midge, very pleased with her choice.

The Word 'this' also functions as an adverb, usually modifying an adjective.

Example: I can't afford shoes this expensive.