In this article, we investigated the thermoformability of poly(lactic acid) (PLA) films with various D-Lactide contents and therefore different crystallization properties, performing tensile and ball burst tests at various temperatures and testing rates. We found that the behavior of the PLA films tested above the glass transition temperature significantly differs due to the difference in D-Lactide content, and thus crystallinity. During tensile testing, elevated temperatures and mechanical stress caused the crystallization temperature to decrease and thus highly induced crystallization. At the same time, as testing speed was increased, the ability of the polymer to crystallize decreased. In ball burst tests, the PLA films crystallized more than during tensile testing. We described the differences found between tensile testing and ball burst testing, which latter better represents the conditions of thermoforming through inducing biaxial deformation.