GoPro, the American action camera company that went public in June, raising $427 million, says it is planning a secondary offering worth a total of $800 million. Existing shareholders would sell shares worth $700 million and the balance of $100 million would come from newly issued shares. The additional funds would be used to invest in people, products, potential acquisitions and infrastructure, said the founder and chief executive, Nick Woodman, who currently owns about 44 percent of the voting shares. GoPro's share price has increased since the IPO from $24 to nearly $80, although it has been trading erratically for several reasons. It went down to around $75 after the announcement of the secondary offering.