Extract page range
pdftk <source-file> cat <start>-<end> output <dst-file>
count number of pages in pdf files in current dir
snatched parts from https://apple.stackexchange.com/a/198860
exiftool *.pdf | awk -F": " '/Page Count/{print $2}' | tr '\n' + | sed 's#+$#\n#' | bc