Hydrolyzes the second messenger cAMP, which is a key regulator of many important physiological processes. {ECO:0000269|PubMed:15260978, ECO:0000269|PubMed:15576036, ECO:0000269|PubMed:9371713}. This is the function of Ensembl gene identifier ENSG00000113448 (PDE4D, phosphodiesterase 4D).