Poly(methyl methacrylate) (PMMA) surfaces have been modified by dynamic plowing lithography. The resulting modified structures, presenting regions of different densities and stiffnesses, have been studied by force-displacement curves. The elasto-plastic response, the stiffness, and the adhesion of the modified samples have been characterized. Force-displacement curves are able to distinguish between unmodified PMMA and two different structures resulting from the lithography, i.e. compressed PMMA and low density PMMA. In particular, the low density regions are made up of cluster-like globular particles, whose elasto-plastic response and adhesion are measured and whose contribution to the total elasto-plastic response and to the adhesion has been studied in detail.