So-called patent trolls have long been shrouded in secrecy. The Federal Trade Commission is hoping its subpoena power can change that. The U.S. competition-regulator announced last month that it would open an investigation into 25 patent assertion entities (PAEs) — derisively known as patent trolls. It is attempting to gather previously unknown information on the operations of the controversial businesses that use patents to file lawsuits rather than make products. Coupled with national ad campaigns and …