exemple un peu terre à terre;
pages=$(awk '/Pages/{print $NF}' < <(pdfinfo "/ext/fanny/Desktop/Thermomix/Thermomix - La France Gourmande.pdf"))
pdfseparate "/ext/fanny/Desktop/Thermomix/Thermomix - La France Gourmande.pdf" recette-%d.pdf
if [ "$((pages%2))" -eq 0 ]; then
unset c; for ((i=1; i<=$pages; i=i+2)); do j=$i; ((j++)); ((c++)); pdfunite recette-"$i".pdf recette-"$j".pdf new-"$c".pdf; done
else
((pages--))
unset c; for ((i=1; i<=$pages; i=i+2)); do j=$i; ((j++)); ((c++)); pdfunite recette-"$i".pdf recette-"$j".pdf new-"$c".pdf; done
((pages++))
mv recette-"$pages" new-"$pages" # reliquat
fi
