# \Ac command not defined [duplicate]

I use acronym package in my Latex file. Strangely, some of its commands, like \Ac are not defined when I compile my file. The \ac command works fine though.

\documentclass[12pt]{extarticle}
\usepackage[printonlyused]{acronym}
\usepackage{multicol}

\title{Physical Layer Security}

\begin{document}
\maketitle
\Ac{BER} is a metric.

\section{Acronyms}
\begin{multicols}{2}
\begin{acronym}
\acro{BER}{bit-error rate}
\end{acronym}
\end{multicols}

\end{document}


And here is the error I see:

! Undefined control sequence. \Ac

• Welcome to TeX.SE! Thank you for including a minimal working example and the text of your error message. I'm sure it won't be long before someone can help you. – dgoodmaniii Nov 13 '19 at 13:07
• Actually, even sooner: somebody's already answered this question. tex.stackexchange.com/questions/80003/… – dgoodmaniii Nov 13 '19 at 13:19
• You are probably using an old version of the package acronym. Take a look into the log file. The version should be 1.42 or higher. This version is on CTAN since yesterday – gernot Nov 13 '19 at 17:14
• I have the latest version of the acronym package with MikTeX updated this morning and the compilation is not finished. – AndréC Nov 13 '19 at 18:09
• What does the log file say? – gernot Nov 13 '19 at 18:17

You have to use version 1.42 of package acronym or higher for \Ac to work.

To check, take a look into the log file. You should find a line there that reads

Package: acronym 2019/11/11 v1.42 Support for acronyms (Tobias Oetiker)


If you get the error Undefined control sequence. \Ac, it is likely that you will find

Package: acronym 2015/03/21 v1.41 Support for acronyms (Tobias Oetiker)