A formation document is simply the document that was filed to create a business entity (e.g. a corporation, a limited liability company, etc.) The name and substance of the document will vary by state, but common examples of formation documents are the Articles of Incorporation, Articles of Organization, Certificate of Incorporation, etc.
The formation documents contain basic information, and which may include the following:
Principal Office Address
Name and Address of the Registered Agent
Authorized Stock (corporations)
List of Officers/Directors (corporations)