The purpose of this open-label, single center trial is to assess the effect of twice daily nebulized ensifentrine (3 mg) on COPD symptoms measured by the COPD Assessment Test (CAT™) scores over 12 weeks in subjects with symptomatic, moderate to severe COPD, taking maintenance LAMA/LABA or LAMA/LABA/ICS therapy. Subjects will continue the maintenance treatment during study participation.