The New York Times added more than 40,000 digital subscribers in the third quarter but advertising revenue continued to slide. The New York Times Co. said Thursday that it posted a net profit of $15.7 million in the quarter which ended in September compared with a loss of $4.3 million in the same quarter a year ago. Revenue declined 3.1 percent to $537.2 million at the Times Co., which owns The Boston Globe, International Herald Tribune and About.com in addition to the flagship New York Times. Total advertising revenue was down 8.8 percent to $262 million while circulation revenue increased 3.4 percent to $237 million. Print advertising revenue fell 10.4 percent in the quarter while digital advertising revenue was down 4.5 percent. The Times Co. said it had 324,000 paid subscribers to digital versions of the newspaper at the end of the third quarter compared with 281,000 at the end of the second quarter. \"Our digital subscription initiatives remained our top focus in the third quarter,\" Times Co. president and chief executive Janet Robinson said. \"We made significant progress in developing a robust digital subscription revenue stream,\" Robinson said in a statement. \"Despite a challenging advertising environment, our operating profit grew reflecting our strong cost performance and growth in circulation revenues.\" The Times Co. posted an operating profit of $33.0 million in the quarter compared with an operating profit of $9.0 million in the same quarter a year ago. Like other US newspapers, The New York Times has been struggling with declining print advertising revenue, falling circulation and the migration of readers to free news online. The Times began charging in March for full access to NYTimes.com and it launched a subscription-only website for The Boston Globe on Wednesday. In a conference call with financial analysts, Robinson said NYTimes.com received more than 47 million unique visitors in August. \"NYTimes.com has maintained its strong traffic and its ranking as a top five news and information site, she said. Robinson said page-view declines for the site were \"less than we projected\" and had dropped an average of 11 percent since the Times began charging online readers in March. She said there had been 7.3 million downloads of the newspaper\'s iPhone news application and 2.8 million downloads of its iPad news app.