diff --git a/doc/rst/conf.py b/doc/rst/conf.py
index aad1df4e..19a2080a 100644
--- a/doc/rst/conf.py
+++ b/doc/rst/conf.py
@@ -28,6 +28,7 @@
 extensions = [
     'sphinx.ext.todo',
     'sphinx.ext.githubpages',
+    'sphinx_simplepdf',
 ]
 
 # Add any paths that contain templates here, relative to this directory.