I got this to work.

my $tmp_dir='/data/documents/';
while (my $ref = $query->fetchrow_hashref()) {
   print "url: $ref->{url}\n";
    my $id = $ref->{document_id};
    my $dir = "/data/documents/";
   # mkdir $dir or die $!;
    my $ff = File::Fetch->new(uri => $ref->{url});
    $ff->fetch( to => $dir );
 rename("$tmp_dir/document.pdf", "$tmp_dir$id.pdf") || die ( "Error in
+ renaming" );
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