This study is open to adults who are at least 40 years old and have idiopathic pulmonary fibrosis (IPF). People can participate in the study if they have a forced vital capacity (FVC) greater than or equal to 45% of the predicted value and fibrosis of 20% or more confirmed by a high-resolution computed tomography (HRCT) scan. The purpose of this study is to find out if a medicine called BI 765423 can improve lung function in people with IPF. The study will compare BI 765423 with a placebo to see if there is a difference in lung capacity after 3 months of treatment and will also look at changes in certain markers related to lung health.

Participants are put into two groups randomly, which means by chance. One group receives the study medicine, and the other group receives a placebo. Placebo looks like BI 765423 but does not contain any study medicine. The study medicine is given as an infusion into a vein every four weeks.

Participants are in the study for 8-10 months. During the study, participants may continue their regular treatment for IPF. During the study they visit the study site several times for screening, treatment, and follow-up. Doctors regularly test lung function by measuring FVC and take blood samples to measure study endpoints. The results are compared between the two groups to see whether the treatment works. The doctors also check participants' health and take note of any unwanted effects.

Inclusion Criteria :

1. 40 years of age or older at the time of informed consent signature.

2. Signed and dated written informed consent in accordance with International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use - Good Clinical Practice (ICH-GCP) and local legislation prior to admission to the trial.

3. Male or female patients. Male patients with Woman of childbearing potential (WOCBP) sexual partners must use contraception (male condom) to avoid exposure via seminal fluid during treatment and for a specific period after last drug intake. Women can only be included if they are of non-childbearing potential, defined as meeting at least one of the below conditions:

   • Permanently surgically sterilised (hysterectomy, bilateral salpingectomy and/or bilateral oophorectomy)

   • Postmenopausal, defined as no menses for 12 months without an alternative medical cause. In questionable cases of postmenopausal status:

     • Women not using sex hormone medication such as hormone replacement therapy may be included if a blood sample confirms levels of follicle stimulating hormone (FSH) > 40 U/L and estradiol < 30 ng/L"

4. Patients with a documented diagnosis of IPF prior to Visit 1, confirmed by the investigator as per the 2022 American Thoracic Society (ATS)/European Respiratory Society (ERS)/Japanese Respiratory Society (JRS)/Latin American Thoracic Association (ALAT) Guideline and, if available, surgical lung biopsy or transbronchial lung cryobiopsy histopathology report.

5. Patients with a high-resolution computed tomography (HRCT) taken within 12 months of Visit 1 (or during the screening period, if not available) confirming "UIP" or "probable UIP" HRCT pattern consistent with the clinical diagnosis of IPF by central review (prior to Visit 2).

   • Patients with an "indeterminate" HRCT finding are eligible if a clinical diagnosis of IPF can be confirmed based on an historical histopathology report of a surgical lung biopsy or cryobiopsy demonstrating a "UIP" or "Probable UIP" pattern.
   • Patients with an "alternative diagnosis" HRCT finding are eligible if a clinical diagnosis of IPF can be confirmed based on an historical histopathology report of a surgical lung biopsy or cryobiopsy demonstrating a "UIP" pattern."

6. Patients with an extent of fibrosis ≥20% as per an HRCT of the chest performed within 12 months prior to Visit 1 or during the screening period (if not available) and confirmed by central review.

7. Patients with a Forced vital capacity (FVC) ≥45% predicted at Visit 1. Predicted normal values will be calculated according to Global Lung Initiative (GLI).

8. Patients with haemoglobin-corrected diffusing capacity of the lungs for carbon monoxide (DLCO) ≥20% predicted at Visit 1.

Further inclusion criteria apply.

Exclusion criteria:

1. Acute exacerbation of IPF within at least 12 weeks prior to Visit 1 and/or during the screening period (investigator-determined).

2. Relevant airways obstruction (pre-bronchodilator forced expiratory volume in 1 second (FEV1)/FVC <0.7) at Visit 1.

3. Lower respiratory tract infection requiring treatment within 4 weeks prior to Visit 1 and/or during the screening period.

4. Significant PH defined by any of the following:

   • Previous clinical or echocardiographic evidence of significant right heart failure according to investigator's judgement
   • History of right heart catheterisation showing a cardiac index ≤2 L/min/m^²
   • PH requiring parenteral therapy with prostanoids

5. On nintedanib or pirfenidone treatment for less than 12 weeks prior Visit 1, planning to start nintedanib or pirfenidone within the first 12 weeks of investigational medicinal product (IMP) treatment or on combined nintedanib plus pirfenidone treatment. Newly diagnosed patients considered in need of SoC treatment by the treating physician, who would be withheld SoC treatment only for the sake of participation in the trial, should also be excluded.

6. Cardiovascular comorbidities including

   • Severe hypertension (uncontrolled under treatment≥160/100 mmHg at multiple occasions) within 3 months of Visit 1
   • Myocardial infarction, stroke, or transient ischemic attack within 6 months of Visit 1
   • Unstable cardiac angina within 6 months of Visit 1

7. Life expectancy for any concomitant disease other than IPF <2.5 years (investigator assessment).

Further exclusion criteria apply.

Once the criteria in section 'time frame' are fulfilled, researchers can use the following link https:// www.mystudywindow.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'spublication plan); 2. and upon signing of a legal agreement.