Remove pdf link border

 cf: https://stackoverflow.com/questions/544907/remove-boxes-from-hyperlinked-toc-in-latex

Add into preamble:

\hypersetup{%

    pdfborder = {0 0 0}
}  

More,

\hypersetup{
    colorlinks,
    citecolor=black,
    filecolor=black,
    linkcolor=black,
    urlcolor=black
}