diff --git a/main/exercise/exercise_show.php b/main/exercise/exercise_show.php
index b864676c6f..62cd22fe7d 100755
--- a/main/exercise/exercise_show.php
+++ b/main/exercise/exercise_show.php
@@ -974,6 +974,9 @@ echo $total_score_text;
 
 if ($action == 'export') {
     $content = ob_get_clean();
+    // needed in order to mpdf to work
+    ob_clean();
+
     $params = array(
         'filename' => api_replace_dangerous_char(
             $objExercise->name.' '.
diff --git a/main/inc/lib/pdf.lib.php b/main/inc/lib/pdf.lib.php
index 6cb0cc5848..6206f6710b 100755
--- a/main/inc/lib/pdf.lib.php
+++ b/main/inc/lib/pdf.lib.php
@@ -88,7 +88,7 @@ class PDF
      * @param $content
      * @param bool|false $saveToFile
      * @param bool|false $returnHtml
-     * @param bool $addDefaultCss
+     * @param bool $addDefaultCss (bootstrap/default/base.css)
      *
      * @return string
      */
@@ -524,7 +524,6 @@ class PDF
             $pdf_name = api_replace_dangerous_char($pdf_name);
             $output_file = $pdf_name.'.pdf';
         }
-        //$this->pdf->Output($output_file, $outputMode); // F to save the pdf in a file
 
         if ($outputMode == 'F') {
             $output_file = api_get_path(SYS_ARCHIVE_PATH).$output_file;