Positronium annihilation lifetime spectroscopy (PALS) using a positron beam is a proven technique to characterize porosity in amorphous thin film materials. The capability to control the depth of the implanted positrons is unique to beams as compared to traditional bulk PALS techniques. By increasing the positron beam energy, positrons are implanted deeper into the film. Control of the positron implantation depth in beam-PALS allows analysis of sub- micron films, investigation of depth-dependent film inhomogeneities, determination of pore interconnection lengths, and access to buried films under barrier layers. Details on PALS depth profiling and an example of applying the technique to a plasma-enhanced-chemical-vapor- deposited (PECVD) porous film are presented.