When is a pronoun is a noun substitute?

A pronoun is always a noun substitute, that is the job of a pronoun.

A pronoun is a Word that takes the place of a noun in a sentence.

We use pronouns when we don't want to keep repeating the same noun when referring to someone or something.

Examples:

I visited The Statue of Liberty on my trip. The Statue of Liberty is very tall, but you can climb to the top of The Statue of Liberty.

Or:

I visited The Statue of Liberty on my trip. It is very tall, but you can climb to the top of it.

Jack and Jill's baby was two months old when I went to visit Jack and Jill and to see Jack and Jill's baby.

Or:

Jack and Jill's baby was two months old when I went to visit them and to see their baby.

Everyone was present when the meeting started. (the indefinite pronoun 'everyone' takes the place of the names of all the people at the meeting)