The filing must disclose the source and amount of funds used for the purchase, the filer's background, and its purpose, including any plans relating to an extraordinary transaction, changes to the board or management, or other actions that would affect control of the company. A material change to the information disclosed requires a prompt amendment, which current SEC rules generally require within two business days.
An investor who initially files passively on Schedule 13G but later develops control intentions must switch to Schedule 13D. That transition from 13G to 13D is itself a signal that the investor's posture has shifted from passive to active.