– This appears to be a Guatemalan secondary school physics textbook (for Tercero Básico , roughly 9th grade). It is likely still under copyright, so free PDFs may not be legally available unless the author or publisher has released it openly. Many unofficial “PDF” sites offering it could be infringing.
Mario Samuel Fernández R. is a prominent author of educational textbooks in Guatemala, specializing in physics for secondary and diversified education. His work, particularly " Física Fundamental – This appears to be a Guatemalan secondary
If your child is searching for "Mario Samuel Fernandez R Fisica Fundamental Tercero Basico PDF," it is usually a sign of poor planning or financial stress. – This appears to be a Guatemalan secondary