Issue #3036845: Call watchdog() when pdftk not properly installed

fillpdf.module

@@ -1546,8 +1546,14 @@ function fillpdf_execute_merge($method, array $fields, $fillpdf, $mode = 'url',
       ob_start();
       passthru(implode(' ', $pdftk_command));
       $data = ob_get_clean();
+
+      $error = NULL;
       if ($data === FALSE) {
-        drupal_set_message(t('pdftk not properly installed. No PDF generated.'), 'error');
+        $error = t('pdftk not properly installed. No PDF generated.');
+      }
+      if ($error) {
+        drupal_set_message($error, 'error');
+        watchdog('fillpdf', $error, array(), WATCHDOG_ERROR);
       }
       file_unmanaged_delete($xfdffile);
       break;