I just got a new computer and installed mikTeX, emacs and auctex.
Then I tried to compile a basic example from mdframed documentation :
\documentclass{article}
\usepackage{amsmath}
\usepackage[dvipsnames]{xcolor}
\usepackage{pstricks}
\usepackage[framemethod=PSTricks]{mdframed}
\begin{document}
Bla!
\mdfsetup{skipabove=\topskip,skipbelow=\topskip}
\newrobustcmd\ExampleText{%
An \textit{inhomogeneous linear} differential equation has the form
\begin{align}
L[v ] = f,
\end{align}
where $L$ is a linear differential operator, $v$ is the dependent
variable, and $f$ is a given non−zero function of the independent
variables alone.
}
\global\mdfdefinestyle{exampledefault}{%
linecolor=red,middlelinewidth=3pt,%
leftmargin=1cm,rightmargin=1cm
}
\begin{mdframed}[style=exampledefault,roundcorner=5]
\ExampleText
\end{mdframed}
\end{document}
I compile using dvips and ps2pdf : In auctex : Command -> TeXing options -> PDF from DVI -> dvips + ps2pdf
I got the same error several times in the log file :
./[activite]-trajectoire.tex:34: Undefined control sequence. \c@lor@to@ps ->\PSTricks _Not_Configured_For_This_Format l.34 \end{mdframed}
I suspect a configuration problem related with mikTeX but didn't find anything.

non−zerois not a hyphen but U+2212 and gives an error too. – Ulrike Fischer Mar 28 '19 at 08:16xelatexto obtain a pdf. – Ignasi Mar 28 '19 at 10:25