As for the PDF version, I can suggest some possible sources where you can find a free PDF of "La culpa es de la vaca" or similar stories:
El libro , compilado por Jaime Lopera y Marta Inés Bernal, es una adaptación de la famosa obra de liderazgo y superación personal diseñada específicamente para el público infantil.
The enduring popularity of this text for children lies in its narrative structure. Unlike didactic lectures on responsibility, the fables allow children to identify behaviors in characters rather than feeling personally attacked.