The demonstrative pronouns dieser (this), jener (that), and solcher (such) replace the article and are also declined.
The pronouns dieser and jener follow the declension pattern of the definite article and fully replace it:
Diesen Mann möchte ich nie mehr sehen! – I never want to see this man again!
Hast du über jenes Kind gesprochen? – Did you talk about that child?
The pronoun solcher is declined like an adjective and used with the indefinite article (in plural without an article):
Ich möchte bitte eine solche Tasche. – I'd like such a bag, please.
Solche verantwortungslosen Eltern haben wir nie gesehen! – We’ve never seen such irresponsible parents!
The demonstrative pronouns es, das (this/it) and selbst (self) are not declined.
Das ist doch mein Portemonnaie! – But this is my wallet!
Ich kann das selbst schaffen. – I can manage that myself.
In compound demonstrative pronouns like derselbe (the same), dieselbe, dasselbe, dieselben, derjenige (the one), diejenige, dasjenige, both parts are declined: the first like a definite article, the second like a weak adjective.
Ich arbeite in demselben Unternehmen. – I work in the same company.
The pronouns der, die, das, dieser, jener, solcher and the compound demonstratives derselbe (the same), dieselbe, dasselbe, dieselben often replace not only the article but also the noun itself, i.e., they are used independently:
Der ist mein Lieblingsstuhl. – This one is my favorite chair.
Diese sind sehr lecker. – These ones are very tasty.
Dieselben kosten zu viel – The same ones cost too much.