The document that is always needed in order to form a corporation is called the "articles of incorporation." These are sometimes called by other names such as "certificate of incorporation" or "articles of association." This is essentially a contract between the corporation and the state that recognizes the existence of the corporation and makes it (in a legal sense) a "person."
The articles, once filed, become the corporation's charter. They include details about the corporation such as the name(s) and address(es) of the people incorporating the firm and the firm's plans for how much stock and what kind of stock will be issued. The charter is part of the public record.