Highlights from the Pierre Auger Observatory and prospects for AugerPrime

The Pierre Auger Observatory has collected data for more than 15 years, accumulating the world's largest exposure to ultrahigh energy cosmic rays (UHECRs). The energy spectrum of the UHECRs has been measured up to $10^{20.2}$ eV, and their mass composition has been studied exploiting both the fluorescence and surface detectors of the Observatory. The analysis of the UHECRs arrival directions allowed us to measure their large-scale anisotropies over more than three decades in energy. The searches for intermediate-scale anisotropies are being performed with an exposure now reaching approximately $100,000$ km$^2$sr yr. For the first time, the fluctuations in the number of muons in inclined air showers above $4 \times 10^{18}$ eV have been obtained, while more information in the energy range $10^{17.5}-10^{18.3}$ eV comes from the direct measure of muons with the underground scintillators of the Observatory. Moreover, we discuss the limits obtained on the fluxes of neutral particles and the results of the searches for UHE neutrinos from transient astrophysical sources. The new perspectives opened by the current results call for an upgrade of the Observatory, whose main aim is the collection of new information about the primary mass of the highest energy cosmic rays to understand the origin of the observed flux suppression. The progress of the upgrade of the Observatory, AugerPrime, is presented and discussed.