documentclass[12pt,letterpaper]{report}

usepackage{sectsty}
usepackage[utf8x]{inputenc}
usepackage{ucs}
usepackage[spanish]{babel}
usepackage{amsmath}
usepackage{amsfonts}
usepackage{amssymb}
usepackage{graphicx}
usepackage[left=3cm,right=2cm, top=3cm, bottom=3cm]{geometry}
usepackage[autostyle, spanish=mexican]{csquotes}

usepackage[authoryear]{natbib} %Bibliografía
bibliographystyle{humannat} %
usepackage{hyperref}

hypersetup{colorlinks, citecolor=blue}
makeatletter
AtBeginDocument{
renewcommandNAT@open{color{blue}(}}
makeatother

begin{document}
This is the text of the document which includes cite{examples} and citep{examples} from a
.bib document saved in the same folder of the .tex document.
bibliography{Bibliografia}
end{document}

documentclass[12pt,letterpaper]{report}

usepackage{sectsty}
usepackage[utf8]{inputenc}
usepackage[spanish]{babel}
usepackage{amsmath}
usepackage{amsfonts}
usepackage{amssymb}
usepackage{graphicx}
usepackage[left=3cm,right=2cm, top=3cm, bottom=3cm]{geometry}
usepackage[autostyle, spanish=mexican]{csquotes}

usepackage[style=authoryear, backend=biber]{biblatex}
usepackage{hyperref}

hypersetup{colorlinks, citecolor=blue}

addbibliograhphy{Bibliografia.bib}

begin{document}
This is the text of the document which includes cite{examples} and parencite{examples} from a
.bib document saved in the same folder of the .tex document.
printbibliography
end{document}

pdflatex paper
 biber paper
 pdflatex paper
 pdflatex paper