diff --git a/dev/resources/iso-normes/facturx-zugferd/README.txt b/dev/resources/iso-normes/facturx-zugferd/README.txt
index 857af0d407b..6861ff856ad 100644
--- a/dev/resources/iso-normes/facturx-zugferd/README.txt
+++ b/dev/resources/iso-normes/facturx-zugferd/README.txt
@@ -1 +1,3 @@
 See https://github.com/atgp/factur-x
+
+See also samples of PDF in https://github.com/dolicloud/dolimods/htdocs/facturxutil/doc