The purpose of this Phase III study is to evaluate the long-term safety and tolerability of two fixed-dose combinations of inhaled aclidinium bromide/formoterol fumarate, aclidinium bromide, formoterol fumarate and placebo in patients with moderate to severe Chronic Obstructive Pulmonary Disease (COPD). Long-term efficacy, pharmacoeconomic and health-related quality of life assessments will also be evaluated. This extension study will include a 28 week treatment period, followed by a four week follow up visit. All patients will remain in the same treatment group as for the lead-in study and continue on one of the four treatment arms or placebo.