Bill Ackman made a big bet on himself even as some investors were second-guessing the future of his hedge fund, Pershing Square Capital Management. So far, it’s paying off. The billionaire plowed about $500 million into the publicly traded arm of his fund last year, arguing it was significantly undervalued. At the time, Pershing Square Holdings Ltd. was trading at roughly $15 a share. The fund has returned 54.5% on its investments this year through August, fueling a 48% gain for shares of Pershing Square Holdings, which traded Friday at $19.10 in Amsterdam, the highest since January 2016.