Packaging Corp. of America shares have surged to a fresh record after the cardboard-box maker surprised Wall Street—and its own executives—by reporting record production and a 26% jump in third-quarter sales. The results come amid doubts about the health of the economy and the strength of the U.S. consumer and lifted shares of rivals International Paper and Smurfit Westrock, both of which are scheduled to report their own results next week. Packaging Corp.'s results also suggest broad U.S. economic strength.