Your code assumes getPageText() returns an empty string when there are no text blocks in the PDF. This is probably an incorrect assumption. In general, a function in list context could be returning a false (-1), an undef or a string with whitespace. (tab, cr, etc). Try this:

{
   my $foo = $doc->getPageText($_) ;
   print $_ unless (defined $foo &&    # Returned something and,
       $foo =~ m/[[:alnum:]]+/ms );  # actually returned text
}
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