1 Pulmonary fibrosis refers to scarring of the lung tissue (fibrosis of the lungs). 2  Symptoms of pulmonary fibrosis include. 3  cough, 4  shortness of breath or difficulty breathing, and. 5  decreased exercise tolerance. 6  The most common type of pulmonary fibrosis is called idiopathic pulmonary fibrosis; its cause is not understood.