Here's an example. Note that you have to export the functions that you want to use without a fully qualified name, and your methods can't reference self (or, you have to check if $self is defined before using it, which means your code will operate differently in function or method mode).

use warnings;
use strict;

package Obj;

use Exporter qw(import);
our @EXPORT_OK = qw(foo);

sub new {
    return bless {}, shift;
}
sub foo {
    my $self;
    if ($_[0] eq __PACKAGE__ || ref $_[0] eq __PACKAGE__){
        $self = shift;
    }
    my ($x, $y) = @_;
    return $x * $y;
}
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The script:

use warnings;
use strict;
use feature 'say';

use lib '.';

use Obj qw(foo);

my $o = Obj->new;

say $o->foo(2, 2);
say Obj::foo(2, 2);
say foo(2, 2);
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Output:

4
4
4
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