APERO: A PipelinE to Reduce Observations -- Demonstration with SPIRou

With the maturation of near-infrared high-resolution spectroscopy, especially when used for precision radial velocity, data reduction has faced unprecedented challenges in terms of how one goes from raw data to calibrated, extracted, and corrected data with required precisions of thousandths of a pixel. Here we present APERO (A PipelinE to Reduce Observations), specifically focused on SPIRou, the near-infrared spectropolarimeter on the Canada--France--Hawaii Telescope (SPectropolarim\`etre InfraROUge, CFHT). In this paper, we give an overview of APERO and detail the reduction procedure for SPIRou. APERO delivers telluric-corrected 2D and 1D spectra as well as polarimetry products. APERO enables precise stable radial velocity measurements on sky (via the LBL algorithm), good to at least ~2 m/s over the current 5-year lifetime of SPIRou.