Inclusion Criteria:  Subject is ≥18 years Subject has received either a single or double lung transplant Subject or Legally Authorized Representative has provided written or electronic informed consent in a manner approved by the applicable Institutional Review Board (IRB) or Ethics Committee Subject is able to perform and willing to comply with the study visits, laboratory assessments, and other study-related procedures Females of child-bearing potential must be non-lactating, must have a negative pregnancy test at screening, and must agree to be abstinent or to use contraception until 30 days after the last dose of PC945 or of SoC anti-mold prophylaxis or pre-emptive therapy  6a. Cohort 1 (de novo prophylaxis immediately post transplant): subject must be ready to be randomized and start anti-mold prophylaxis within 48 hours of returning to the intensive care unit (ICU) after the transplant surgery or  6b. In Cohort 2 (pre-emptive therapy): subject must meet all of the following:  Aspergillus spp. colonization of the respiratory tract confirmed within 91 days (13 weeks) after a lung transplant. Colonization is defined according to the 2010 ISHLT Consensus Statement definition criteria for colonization Without evidence of pulmonary fungal disease Must be ready to start anti-mold medication within 72 hours after the positive culture(s), galactomannan or PCR result(s) were reported  Exclusion Criteria:  Subject who would normally receive nebulized amphotericin B as the only mold active antifungal agent as initial SoC prophylaxis or pre-emptive therapy Subject with a fungal disease requiring systemic antifungal treatment at the time of transplant Subject has received a mold active antifungal agent post transplant (Note: a subject who receives a mold active antifungal agent within 24 hours before, during, or after the transplant procedure will not be excluded if the mold active medication was stopped within 48 hours of returning to the ICU after the transplant surgery, or prior to randomization (whichever happens first) Subject who has previously received PC945 Subject who is receiving, or who is due to receive at any time during the study, an investigational medicinal agent Subject who is participating, or who is due to participate at any time during the study, in a therapeutic or diagnostic clinical trial Subject has an endobronchial stent in situ Subject with a known history of allergy, hypersensitivity, or any previous serious reaction to any component of the PC945 formulation, azoles, echinocandins, or amphotericin B Subject with an elevated alanine transaminase (ALT) or, aspartate transaminase (AST) >5 x the upper limit of normal (ULN) Subject with any known history or current evidence of alcohol or drug abuse that, in the Investigator's opinion, would exclude the subject from participation in the study Subject with a concomitant medical condition or post-surgery complication that, in the opinion of the Investigator, may jeopardize adherence to the protocol requirements or impede the accurate measurement of efficacy or may be an unacceptable additional risk to the subject should he/she participate in the study Subject's life expectancy is not expected to be sustained for the duration of the trial (16 weeks), in the opinion of the investigator In Cohort 2 (pre-emptive therapy), subject colonized with a documented azole-resistant Aspergillus organism or with any non-Aspergillus mold