Adsorption, interaction, and diffusion of adatoms on surfaces control growth and relaxation of epitaxial nanostructures and nanofilms. Previous reports of key diffusion barriers for Pb diffusion on low-index Pb surfaces are limited in scope and accuracy. Thus, we apply density functional theory (DFT) to calculate the adsorption and diffusion energetics for a Pb adatom on Pb(111), Pb(100), and Pb(110) nanofilms with different thicknesses. We find that these quantities exhibit damped oscillatory variation with increasing film thickness. For Pb(111) films, energetics along the minimum energy path for Pb adatom diffusion between adjacent fcc and hcp sites varies significantly with film thickness, its form differing from other metal-on-metal(111) systems. For Pb(111) and Pb(100) nanofilms, diffusion barriers obtained for both adatom hopping and exchange mechanism differ significantly from previous DFT results. Hopping is favored over exchange for Pb(111), and the opposite applies for Pb(100). For Pb(110) nanofilms, Pb adatom hopping over an in-channel bridge is most facile, then in-channel exchange, then cross-channel exchange, with cross-channel hopping least favorable. We also assess lateral Pb adatom interactions, and characterize island nucleation during deposition on Pb(111).