This goes into a small plugin and into the folder mu-plugins ... User can now only upload images and pdf

restrict-upload.php

<?php add_filter('upload_mimes','restrict_mimes_for_subscriber');
function restrict_mimes_for_subscriber($mimes) {
  if (!current_user_can('read')) {
    return;
  }
  
  $mimes = array(
			'pdf' => 'application/pdf',
			'jpg|jpeg' => 'image/jpeg',
			'png' => 'image/png',
			'gif' => 'imgage/gif'
		);
		
	return $mimes;

}
?>