This study focuses on people who have been diagnosed with invasive pulmonary aspergillosis (IPA, a lung infection caused by a common fungus found in the environment called aspergillus) and who are not responding well to their current antifungal therapy. The purpose of the study is to evaluate the safety and effectiveness of an investigational inhaled antifungal drug called opelconazole (PC945 nebulizer suspension) when given in combination with standard-of-care antifungal therapy. The study will also assess how opelconazole is processed in the body including how it is distributed, transformed, and removed, by measuring the levels of opelconazole in the blood and lungs; this is called pharmacokinetics. Opelconazole is designed as an inhaled treatment. Participants will be randomly assigned to 1 of 2 treatment groups: the opelconazole plus standard-of-care antifungal therapy group, or the placebo (inactive substance) plus standard-of-care antifungal therapy group.