Are all pro-forms the same in that they have to have antecedents and postcedents in the conversation to have any meaning? For example, the word "it" derives its meaning from a noun located either just before or just after the pronoun "it". Also, the word "Yes" is a pro-sentence, and it derives its meaning from a statement just said, for example, "Pizza is delicious." and then someone says "Yeah.". Would the person's "Yeah." mean "Yeah, pizza is delicious.", or is the meaning of a pro-form derived from something else?
yes and no. a proform by definition must refer to something else, but that "something else" need not be linguistic. For example, Joe says something crazy. I point my index finger to my temple and swirl it (meaning, that's nutty). Sally points at me and says "he's right" or "that's right" or similar. I haven't said anything, but everybody understands Sally's point.
Brainstorming a bit turns up a lot of examples, it seems. Sometimes it will boil down to definition (are demonstratives pro-forms), but even excluding demonstratives, I can think of quite a lot:
(1) Generic pronouns:
*On* ne sait pas. *3sg.* NEG know NEG. (French) *One* does not know / We can't tell
(2) Speech act participants: I'm a little teaport, short and stout.
(2) Reflexives in nominalised VPs:
不 患 人 之 不 *己* 知 Bu huan ren zhi bu *ji* zhi NEG worry others GEN NEG *self* know (Old Chinese) Do not worry about others' not knowing the *self*
(3) Reciprocals in nominalised VPs: Knowing each other well is important for teamwork.
(4) Pro-sentences in polar questions:
Ana ruwa, *ko*? one.is rain *or* Is it raining or **not**? (Hausa - Schachter and Shopen 2007)
(5) Answers to questions: The original sentence in the OP if it came from this conversation:
A: Is pizza delicious? B: *No*!
Since the statement 'Pizza is not delicious' never appeared in the conversation.
Schachter, P. and Shopen, T. (2007). Parts of speech. In Shopen, T. (ed.), Language typology and syntactic description (Vol. 3). Cambridge: Cambridge University Press.
Most pro-forms will denote things which are more explicitly discussed in the conversation, but some do not.
One example is the English word now, which (IMO) should be analysed as a pro-preposition. Now stands in for a temporal phrase, such as at this moment in time, but only rarely would a speaker also refer to that moment with a full prepositional phrase.