\documentclass[a4paper]{article}
\usepackage[utf8]{inputenc}

\usepackage{tikz}
\usepackage{hyperref}

\IfFileExists{pgfplots.sty}{%
    \usepackage{pgfplots}
}{}%

\IfFileExists{tikzlibraryexternal.code.tex}{%
    \usetikzlibrary{external}
}{%
    \message{TEST IS RUNNING IN COMPATIBILITY MODE}%
    % a test to check for pgf 2.00 compatibility, to check whether the
    % external library copy shipped with pgfplots works:
    \usepgfplotslibrary{external}
}%

\pgfkeys{/pgf/images/include external/.code={\href{file:#1}{\pgfimage{#1}}}}
