Trim the spaces around a pdf file

Hi:

I am not very familiar with perl and the api. After some searches, it
seems be able to return the trimbox of an existing pdf.
e.g.
my ($self)=@_;
my $cropBoxRef=$self->find_prop("CropBox");
if ($cropBoxRef) {
return map {$_->val} $cropBoxRef->elementsof;
}
else {
return $self->get_mediabox();
}
}

Then how can I get the physical coordinates of the trimbox (or othe
ways), in order to clip the actual content

cheers
kenpeter