I need a list of all the subs brought in by the file, not all the subs in the current or main package

You could compare the list of functions before and after requiring the file:

### file.pm
sub funcC {
}
sub funcD {
}
sub funcE {
}
1;

### main script
#!/usr/bin/perl

use strict;
use warnings;
use Devel::Symdump;

sub funcA {
}
sub funcB {
}

sub get_functions {
    return Devel::Symdump->functions("main");
}

my %before = map {$_ => 1} get_functions();

require 'file.pm';

print "$_\n" for sort grep !$before{$_}, get_functions();

__END__
main::funcC
main::funcD
main::funcE
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