NEW YORK—Stocks are opening moderately lower on Wall Street, leaving major indexes well in the red for the week following the biggest pullback for the market in more than two years on Tuesday. Railroad operators were mostly higher after a tentative labor agreement was reached, averting a strike across the country that could have been devastating to the economy. Software maker Adobe fell sharply after announcing a $20 billion acquisition of a design company and issuing a forecast for the current quarter that fell short of what investors were expecting. The S&P 500 was down half a percent in the early going Thursday….