documentclass{scrartcl}

usepackage{hyperref}

makeatletter
renewcommandsectionlinesformat[4]{%
   ifstr{#1}{section}{%
      @hangfrom{hskip#2relax #3}{MakeUppercase{#4}}%
%      @hangfrom{hskip#2relax #3}{texorpdfstring{MakeUppercase{#4}}{#4}}% doesn't work
   }{%
      @hangfrom{hskip#2relax #3}{#4}%
   }%
}
renewcommand{sectionformat}{MakeUppercase}
makeatother

begin{document}
Test
clearpage
addsec{Addsec on page 2}
Text
end{document}