This study will evaluate the impact Nintedanib Solution for Inhalation (AP02) has on lung function and key measures of fibrosis in adult patients with idiopathic pulmonary fibrosis (IPF) as well as assess its safety and tolerability.

Adults 40 years of age or older with IPF who meet the inclusion and exclusion criteria can participate in this study if they are not currently on treatment for IPF, and if treated with oral nintedanib or pirfenidone, have stopped the medication for at least 3 months.

Researchers will compare two different doses of AP02 to a placebo (a look-alike substance that contains no drug) to see if AP02 works to treat IPF. Participants are put into 1 of 3 groups randomly, which means by chance and will take AP02 or a placebo two times every day for 12 weeks by using a nebulizer, which is a device that provides medicine to the lungs via inhalation.

Participants will visit the office 6 times and receive 1 phone call over a 16-week period. At site visits doctors regularly perform breathing tests that measure how well the lungs are working, give the patient questionnaires and will check the participants' health.

Inclusion Criteria:

• Male or female patients aged ≥40 years at the time of signing the written informed consent form
• Diagnosis of idiopathic pulmonary fibrosis (IPF) as defined by American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/ Asociación Latinoamericana de Tórax IPF guidelines within 5 years
• Combination of High-Resolution Computerized Tomography (HRCT) pattern, and if available, surgical lung biopsy pattern consistent with diagnosis of IPF
• In a stable condition and suitable for study participation based on the results of medical history, physical examination, vital signs, 12-lead ECG, and laboratory evaluation
• Forced vital capacity (FVC) ≥45% predicted of normal
• Lung diffusion test (DLCO) corrected for hemoglobin (Hgb) ≥30% and ≤80% predicted of normal.
• Women and men of childbearing potential must use highly effective contraception measures until 90 days after the last dose of study drug.

Exclusion Criteria:

• Current treatment with oral nintedanib, oral pirfenidone, or previous treatment with oral nintedanib or oral pirfenidone within 3 months prior to screening. Participants who have taken both oral nintedanib and pirfenidone together as a treatment will not be able to join the study.
• Forced expiratory volume (FEV) in the first second/FVC (FEV1/FVC) ratio ≥0.7 based on pre-bronchodilator value
• Participants with a history of serious cardiovascular disease, bleeding problems or significant liver or kidney disease (as defined in the study protocol)
• History of diverticular disease or abdominal surgery within 4 weeks prior to screening visit
• History of cancer within the past 5 years (except for certain types explained in the protocol)
• Participants who have smoked within the past 3 months prior to screening, who are not willing to stop smoking during the study, or who currently use illegal drugs or drugs of abuse
• Female participants who are pregnant or nursing
• Use of any investigational drugs including those for IPF within the past 30 days prior to screening

Further inclusion/exclusion criteria apply