A Clinical Study to Test How Effective and Safe GLPG1690 is for Subjects With Idiopathic Pulmonary Fibrosis (IPF) When Used Together With Standard Medical Treatment

Inclusion Criteria:

- Male or female subject aged ≥40 years on the day of signing the ICF.

- A diagnosis of IPF within 5 years prior to the screening visit, as per applicable
ATS/ERS/JRS/ALAT guidelines.

- Chest HRCT historically performed within 12 months prior to the screening visit and
according to the minimum requirements for IPF diagnosis by central review based on
subject's HRCT only (if no LB available), or based on both HRCT and LB (with
application of the different criteria in either situation). If an evaluable HRCT <12
months prior to screening is not available, an HRCT can be performed at screening to
determine eligibility, according to the same requirements as the historical HRCT.

- Subjects receiving local standard of care for the treatment of IPF, defined as either
pirfenidone or nintedanib, or neither pirfenidone nor nintedanib (for any reason).

- The extent of fibrotic changes is greater than the extent of emphysema on the most
recent HRCT scan (investigator-determined).

- Meeting all of the following criteria during the screening period: FVC ≥ 45% predicted
of normal, Forced expiratory volume in 1 second (FEV1)/FVC ≥0.7, DLCO corrected for Hb
≥30% predicted of normal.

- Estimated minimum life expectancy of at least 30 months for non IPF related disease in
the opinion of the investigator.

- Male subjects and female subjects of childbearing potential agree to use highly
effective contraception/preventive exposure measures from the time of first dose of
IMP (for the male subject) or the signing of the ICF (for the female subject), during
the study, and until 90 days (male) or 30 days (female) after the last dose of IMP.

- Able to walk at least 150 meters during the 6MWT at screening Visit 1; without having
a contraindication to perform the 6MWT or without a condition putting the subject at
risk of falling during the test (investigator's discretion). The use of a cane is
allowed, the use of a stroller is not allowed at all for any condition. At Visit 2,
for the oxygen titration test, resting SpO2 should be ≥88% with maximum 6 L O2/minute;
during the walk, SpO2 should be ≥83% with 6 L O2/minute or ≥88% with ≤4 L O2/minute.

Exclusion Criteria:

- History of malignancy within the past 5 years (except for carcinoma in situ of the
uterine cervix, basal cell carcinoma of the skin that has been treated with no
evidence of recurrence, prostate cancer that has been medically managed through active
surveillance or watchful waiting, squamous cell carcinoma of the skin if fully
resected, and Ductal Carcinoma In Situ).

- Acute IPF exacerbation within 6 months prior to screening and/or during the screening
period.

- Lower respiratory tract infection requiring antibiotics within 4 weeks prior to
screening and/or during the screening period.

- Interstitial lung disease associated with known primary diseases (e.g. sarcoidosis and
amyloidosis), exposures (e.g. radiation, silica, asbestos, and coal dust), or drugs
(e.g. amiodarone).

- Diagnosis of severe pulmonary hypertension (investigator- determined).

- Unstable cardiovascular, pulmonary (other than IPF), or other disease within 6 months
prior to screening or during the screening period (e.g. acute coronary disease, heart
failure, and stroke).

- Underwent major surgery within 3 months prior to screening or have major surgery
planned during the study period.

- Abnormal LFT at screening, defined as AST, and/or ALT, and/or total bilirubin
≥1.5xULN, and/or GGT ≥3xULN. Retesting is allowed once.

- Abnormal renal function defined as estimated creatinine clearance, calculated
according to Cockcroft-Gault calculation (CCr) <30 mL/min. Retesting is allowed once.

- Use of any of the following therapies within 4 weeks prior to screening and during the
screening period, or planned during the study: warfarin, imatinib, ambrisentan,
azathioprine, cyclophosphamide, cyclosporine A, bosentan, methotrexate, sildenafil
(except for occasional use), prednisone at steady dose >10 mg/day or equivalent.