/usr/lib/perl5/PDL/add_doc.pl is in libpdl-stats-perl 0.6.2-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | use PDL::Doc;
use File::Copy qw(copy);
# Find the pdl documentation
my ($dir,$file,$pdldoc);
DIRECTORY:
for (@INC) {
    $dir = $_;
    $file = $dir."/PDL/pdldoc.db";
    if (-f $file) {
        if (! -w "$dir/PDL") {
            print "No write permission at $dir/PDL! Not updating docs database.\n";
            exit;
        }
        print "Found docs database $file\n";
        $pdldoc = new PDL::Doc ($file);
        last DIRECTORY;
    }
}
die ("Unable to find docs database! Not updating docs database.\n") unless $pdldoc;
for (@INC) {
    $dir = "$_/PDL/Stats";
    if (-d $dir) {
        $pdldoc->ensuredb();
        $pdldoc->scantree($dir);
        eval { $pdldoc->savedb(); };
        warn $@ if $@;
        print "PDL docs database updated.\n";
        last;
    }
}
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