Poor is an adjective.
However, in English, you can "nounify" many adjectives by using them where nouns are expected.
Doing can indicate you are talking about an entire class of something that has the adjective as an attribute.
Poor can and is often used to refer to an economic class. So it's frequently used as a noun. So you can see and use phrases like:
The poor are frequently at a disadvantage.
There are many poor who cannot partake in much of modern society.
In Africa there are many poor.
However this needs a context where you are talking about economic classes, not individuals.