Issue #1392922: Revert to strlen().

drupal_strlen() appears to be returning an incorrect string length and is thus not the right
  choice in this case.

fillpdf.module

@@ -425,7 +425,7 @@ function fillpdf_merge_pdf($fid, $nids = NULL, $webform_arr = NULL, $sample = NU
   drupal_add_http_header('Expires', 0);
   drupal_add_http_header('Cache-Control', 'must-revalidate, post-check=0, pre-check=0');
   drupal_add_http_header('Content-type', 'application-download');
-  drupal_add_http_header('Content-Length', drupal_strlen($data));
+  drupal_add_http_header('Content-Length', strlen($data));
   drupal_add_http_header('Content-disposition', 'attachment; filename="' . $output_name . '"');
   drupal_add_http_header('Content-Transfer-Encoding', 'binary');
   echo $data;