Add a PDF upload field in AnsPress questions

custom-field.php

<?php

/**
 * Adds a PDF field to AnsPress question form.
 *
 * @param array $form Form arguments.
 * @return void
 */
function my_custom_question_field( $form ) {

  // Upload field.
  $form['fields']['screenshot'] = array(
    'fields' => array(
	'pdf' => array( // This is a unique key for field.
		'label'       => __( 'PDF File' ),
		'desc'        => __( 'Allow single PDF file upload.' ),
		'type'        => 'upload',
		'upload_options' => array(
			'multiple'  => false, // Only allow single image upload.
			'allowed_mimes' => array(
					'pdf' => 'application/pdf', // This will allow uploading of PDF file.
			),
		),
	),
     ),
  );
  return $form;
}
add_filter( 'ap_question_form_fields', 'my_custom_question_field' );

Problem : https://anspress.io/questions/question/how-to-insert-pdf-word-file-on-my-site-2/