diff --git a/op/op.PdfPreview.php b/op/op.PdfPreview.php
index 00fae0395..9f0ad2849 100644
--- a/op/op.PdfPreview.php
+++ b/op/op.PdfPreview.php
@@ -30,6 +30,11 @@ include("../inc/inc.ClassUI.php");
 include("../inc/inc.ClassController.php");
 include("../inc/inc.Authentication.php");
 
+/**
+ * Include class to preview documents
+ */
+require_once("SeedDMS/Preview.php");
+
 $tmp = explode('.', basename($_SERVER['SCRIPT_FILENAME']));
 $controller = Controller::factory($tmp[1], array('dms'=>$dms, 'user'=>$user));