Here's a little Perl program I use for the task. Perl isn't special; it's just a wrapper around pdftk to interpret its dump_data
output to turn it into page numbers to extract:
#!perl
use v5.24;
use warnings;
use Data::Dumper;
use File::Path qw(make_path);
use File::Spec::Functions qw(catfile);
my $pdftk = '/usr/local/bin/pdftk';
my $file = $ARGV[0];
my $split_dir = $ENV{PDF_SPLIT_DIR} // 'pdf_splits';
die "Can't find $ARGV[0]\n" unless -e $file;
# Read the data that pdftk spits out.
open my $pdftk_fh, '-|', $pdftk, $file, 'dump_data';
my @chapters;
while( <$pdftk_fh> ) {
state $chapter = 0;
next unless /\ABookmark/;
if( /\ABookmarkBegin/ ) {
my( $title ) = <$pdftk_fh> =~ /\ABookmarkTitle:\s+(.+)/;
my( $level ) = <$pdftk_fh> =~ /\ABookmarkLevel:\s+(.+)/;
my( $page_number ) = <$pdftk_fh> =~ /\BookmarkPageNumber:\s+(.+)/;
# I only want to split on chapters, so I skip higher
# level numbers (higher means more nesting, 1 is lowest).
next unless $level == 1;
# If you have front matter (preface, etc) then this numbering
# will be off. Chapter 1 might be called Chapter 3.
push @chapters, {
title => $title,
start_page => $page_number,
chapter => $chapter++,
};
}
}
# The end page for one chapter is one before the start page for
# the next chapter. There might be some blank pages at the end
# of the split for PDFs where the next chapter needs to start on
# an odd page.
foreach my $i ( 0 .. $#chapters - 1 ) {
my $last_page = $chapters[$i+1]->{start_page} - 1;
$chapters[$i]->{last_page} = $last_page;
}
$chapters[$#chapters]->{last_page} = 'end';
make_path $split_dir;
foreach my $chapter ( @chapters ) {
my( $start, $end ) = $chapter->@{qw(start_page last_page)};
# slugify the title so use it as a filename
my $title = lc( $chapter->{title} =~ s/[^a-z]+/-/gri );
my $path = catfile( $split_dir, "$title.pdf" );
say "Outputting $path";
# Use pdftk to extract that part of the PDF
system $pdftk, $file, 'cat', "$start-$end", 'output', $path;
}