Blazars are a special type of AGN, with jets that happen to
point very close to the direction towards Earth. The powerful
gamma-ray beam from distant blazars represents a unique tool to
explore the environment along its path, and allows us to probe opacity
both inside the source and in the intergalactic medium. Internally,
gamma-rays experience attenuation due to photon-photon absorption, a
result of interactions with AGN-generated photon fields. This
interaction introduces distinct features in gamma-ray spectra. Upon
exiting the source, gamma-rays encounter attenuation due to the
Extragalactic Background Light (EBL). Understanding and characterizing
these absorption processes not only reveals the complex structure of
blazars and the poorly known gamma-ray emitting zone's location, but
also holds implications for fundamental physics, including axion-like
particles (ALPs). In this work, we perform analysis and physical
modeling of Fermi-LAT data of nine high-redshift (z > 3) blazars, and
search for characteristic features in the gamma-ray spectra induced by
the internal absorption, as well as endeavor to establish stringent
constraints on the EBL, given the high redshift of the blazars under
study.