\documentclass[oneside]{book}
\usepackage[utf8]{inputenc}
\usepackage{fancyhdr}
\usepackage[spanish]{babel}
\usepackage[document]{ragged2e}
\usepackage{lastpage}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathrsfs, amsmath}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{tcolorbox}
\usepackage{cancel}
\usepackage{nccmath}
\usepackage{hyperref,lipsum}
\usepackage{fullpage}
\setlength{\headheight}{12.0pt} % Set the headheight to at least 12.0pt
\addtolength{\topmargin}{-12.0pt} % Adjust topmargin to compensate
\pagestyle{fancy}
\fancyhf{}
\newcommand{\Lagr}{\mathcal{L}}
\lhead[Head 1]{Head 1}
\rhead[Head 2]{Head 2}
\rfoot[Página \thepage]{Página \thepage}
\begin{document}
\input{Portada}
\input{Pregunta 1}
\end{document}
