A comprehensive understanding of the decomposition of perfluoropolyether (PFPE) films is crucial for establishing effective lubrication of heat-assisted magnetic recording (HAMR) systems. In this study, to examine the combined influence of heat, mechanical stress, and water, we conducted nonequilibrium reactive molecular dynamics simulations using our ReaxFF force field for the PFPE D-4OH films mixed with water. We thoroughly analyzed the reaction rates, types, pathways, and products, and identified vulnerable bonds. The results demonstrate that water significantly accelerates the reactions of D-4OH, particularly at lower normal pressures. We found that water molecules form clusters and are surrounded by the D-4OH end groups. Consequently, water induces hydrolysis of D-4OH or catalyzes reactions between D-4OH by dissociating C–O bonds in the end groups.