I think that is a very confusing way to look at things. It's not that we collectively agree that the document means that something exists, but rather this is the category of things for which existence is by definition caused by the existence of those documents. A corporation is not some ethereal thing that exists, and we agree that we are justified in believing it exists because there is a document, but rather the document is effectively the corporation. The thing we as a society agree about is merely linguistic in nature: We agree on the definition of the terms, i.e., we have a common language.
Legally speaking and as far as general people's understanding is concerned, this is incorrect. The document is the license to form the corporation, it does not make up the corporation.
If I could persuade enough people that incorporation documents are invalid and that we all collectively agreed the corporations would cease to exist. This is of course an absurd notion and not practically achievable but there was a time before corporations existed and there could be a time after which they existed if we want. This is the same for any human conceived idea.