Dara Khosrowshahi, the chief executive of Uber, which is racing its rival Lyft to the public markets. : SAN FRANCISCO — Uber confidentially filed paperwork on Thursday to go public, according to two people with knowledge of the matter, officially moving toward what is expected to be one of the biggest and most anticipated tech company stock market debuts ever. The ride-hailing company filed its paperwork with the Securities and Exchange Commission on the same day that its rival Lyft also filed for an offering, said the people, who requested anonymity because they were not authorized to speak publicly.