All you need do is make sure PDFColumn and $page share the same namespace, either by declaring your sub into PDF::Create's ...

sub PDF::Create::PDFColumn {
   my $page   = shift;
   my $params = shift;

   # ...
}
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... or (more elegantly) by sub-classing ...

package PDF::Create::Column;

  # Try looking for any methods not defined here 
  # in PDF::Create instead.
use base qw/ PDF::Create /;

sub PDFColumn {
   my $page   = shift;
   my $params = shift;

   # ...
}

1;
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    --k.