Bookmarking uppercase Roman numbers

Question

Have the MWE:

\documentclass{article}
\usepackage[backref=page,hypertexnames]{hyperref}
\newcommand{\RNum}[1]{\uppercase\expandafter{\romannumeral #1\relax}}

\begin{document}
    \section{Sec. \RNum{1}}
    \section{Sec. \RNum{2}}
\end{document}

The bookmark in the PDF shows that the numbers are indeed small case (while it should be upper case). How to get it fixed?

Answer 1

You need an expandable version of \RNum so that it appears correctly in the bookmarks. But \uppercase is not expandable (see \expandafter with \uppercase), so you will need the slightly different definition from the LaTeX kernel (see also How can I get Roman numerals in text?, thank you to Marcel Krüger for pointing out that the initial answer had just a verbatim copy of \RNum)

\documentclass{article}
\usepackage{hyperref}

\makeatletter
\newcommand*{\RNum}{} % empty def to throw error if name already taken
\let\RNum\@Roman      % actual definition
\makeatother

\begin{document}
    \section{Sec.\ \RNum{1}}
    \section{Sec.\ \RNum{2}}
\end{document}