This study is open to people aged 40 years or older who have at least 1 family member with pulmonary fibrosis. Pulmonary fibrosis is a condition where lung tissue becomes scarred, making it harder to breathe. People can join if a lung scan shows early changes in the lung, called interstitial lung abnormalities, which may lead to lung scarring. People with family members who have pulmonary fibrosis are more likely to develop it themselves. That is why it is important to check early for lung changes and find ways to prevent the condition from getting worse. The purpose of this study is to find out whether a medicine called nerandomilast can help slow down changes in the lung in people with a family history of pulmonary fibrosis.

Participants are put into one of 2 groups randomly, which means the group is chosen by chance. One group takes nerandomilast tablets, and the other group takes placebo tablets. Placebo tablets look like nerandomilast tablets but do not contain any medicine. Participants take a tablet twice a day for about 2 to 3 years. There is a 3 out of 5 chance that participants will receive nerandomilast instead of the placebo.

Participants are in the study for about 2 to 3 years. Participants visit the study site multiple times: more frequently during the first 2 years (about every 3 months), and then every 6 months thereafter. In the 3rd year, participants also have phone calls with the site staff every 3 months.

Doctors regularly test lung function and take chest scans to see if the treatment works. The results are compared between the 2 groups to see if nerandomilast helps. The doctors also check participants' health and take note of any unwanted effects.

Inclusion Criteria:

• Individuals ≥40 years of age at the time of first signed informed consent at Visit 1a
• Participants must have at least 1 first-degree relative (biological parent, sibling, or child) with confirmed pulmonary fibrosis (idiopathic pulmonary fibrosis [IPF], idiopathic nonspecific interstitial pneumonia [NSIP], and/or pulmonary fibrosis due to known genetic cause [e.g. short telomere syndrome, mucin 5B (MUC5B) mutation, surfactant protein mutations])
• High resolution computed tomography (HRCT) scan with evidence of interstitial lung abnormalities involving at least 5% of a single lung zone or interstitial lung disease (ILD), based on central evaluation
• Forced vital capacity (FVC) ≥80% of predicted normal at Visit 1b
• Diffusing capacity of the lungs for carbon monoxide (DLCO) corrected for hemoglobin ≥70% of predicted normal at Visit 1b Further inclusion criteria apply.

Exclusion Criteria:

• Prior known pulmonary fibrosis that, in the opinion of the Investigator, requires treatment with approved therapies
• Prebronchodilator forced expiratory volume in 1 second (FEV1)/FVC <0.7 at Visit 1b
• HRCT findings consistent with probable or definite usual interstitial pneumonia (UIP) pattern
• Any medical condition that is known to predispose to the development of pulmonary fibrosis (e.g. known connective tissue disease)
• Prior or current use of nerandomilast, nintedanib, or pirfenidone Further exclusion criteria apply.

Once the criteria in section 'time frame' are fulfilled, researchers can use the following link https://www.clinicalstudies.boehringer-ingelheim.com/msw/datasharing to request access to the clinical study documents regarding this study, and upon a signed "Document Sharing Agreement". Furthermore, researchers can request access to the clinical study data, for this and other listed studies, after the submission of a research proposal and according to the terms outlined in the website.

One year after the approval has been granted by major Regulatory Authorities and after the primary manuscript has been accepted for publication, or after termination of the development program.

For study documents -upon signing of a 'Document Sharing Agreement'. For study data -1. after the submission and approval of the research proposal (checks will be performed by the sponsor and/or the independent review panel, including checking that the planned analysis does not compete with sponsor's publication plan); 2. and upon signing of a legal agreement.