Study to Evaluate Efficacy/Safety of 4 Doses of CHF5259 Via Dry Powder Inhaler (DPI) in Patients With COPD

Outpatients attending the hospital clinics/study centres will be recruited. Patients with moderate to severe COPD airflow obstruction according to GOLD 2015 criteria. A total of approximately 300 patients will be enrolled. Patients are followed during 3 different treatment periods of 4 weeks separated each by 3 weeks wash-out period. The study lasts approximately 21 weeks for each patient and a total of 11 clinic visits is performed during the study. The primary endpoint is the Forced Expiratory Volume in 1 second (FEV1) Area Under the Curve (AUC) 0-12h normalised by time on Day 28.