Waltham-based Parexel International Corp. surged after the tester of experimental medicines for drug makers forecast third-quarter earnings of up to 32 cents a share, just above the average analyst estimate of 30 cents. The company expects service revenue for the period in the range of $350 to $358 million. For the most recent quarter, Parexel said revenue rose 9.5 percent to $333.2 million, compared with $304.4 million a year ago. Parexel chairman and CEO Josef H. von Rickenbach cited the company’s “positive momentum,’’ and said Parexel is “starting to hit our stride’’ with recently awarded accounts.