This is a Phase IIb, randomized, double blind, chronic dosing (28 days), four period, five treatment, incomplete block, crossover design in subjects with moderate to severe COPD. The overall objective is to demonstrate that the combination of budesonide (BD; PT008) and formoterol fumarate (FF; PT005) in a metered-dose inhaler (MDI); (BFF MDI; PT009) provides benefit on lung function compared with BD MDI in subjects with moderate to severe COPD.