Fix config backend model PDF file name extension

Author: Vinai

app/code/Magento/Config/Model/Config/Backend/File/Pdf.php

@@ -0,0 +1,21 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+namespace Magento\Config\Model\Config\Backend\Image;
+
+/**
+ * @api
+ */
+class Pdf extends \Magento\Config\Model\Config\Backend\File
+{
+    /**
+     * @return string[]
+     */
+    protected function _getAllowedExtensions()
+    {
+        return ['pdf'];
+    }
+}

app/code/Magento/Config/Model/Config/Backend/Image/Pdf.php

@@ -4,16 +4,12 @@
  * See COPYING.txt for license details.
  */
 
-/**
- * System config image field backend model for Zend PDF generator
- *
- * @author     Magento Core Team <[email protected]>
- */
 namespace Magento\Config\Model\Config\Backend\Image;
 
 /**
  * @api
- * @since 100.0.2
+ * @deprecated The wrong file type extensions are returned.
+ * @see \Magento\Config\Model\Config\Backend\File\Pdf
  */
 class Pdf extends \Magento\Config\Model\Config\Backend\Image
 {
@@ -22,6 +18,6 @@ class Pdf extends \Magento\Config\Model\Config\Backend\Image
      */
     protected function _getAllowedExtensions()
     {
-        return ['tif', 'tiff', 'png', 'jpg', 'jpe', 'jpeg'];
+        return ['tif', 'tiff', 'png', 'jpg', 'jpe', 'jpeg', 'pdf'];
     }
 }