Change the default access options for new BP Docs.

bp_docs_filter_default_access_options.php

<?php 
add_filter( 'bp_docs_get_default_access_options', 'my_change_docs_default_access_levels' );
function my_change_docs_default_access_levels( $defaults ) {
  /**
   * Possible access capabilities are 'read', 'edit', 'read_comments', 'post_comments', 
   * 'view_history', or 'manage'.
   * Possible access options are 'loggedin', 'creator', or 'anyone'. 
   * If BuddyPress groups are activated, then additional access options are available 
   * to docs that are associated with a group: 
   * 'group-members' and 'admins-mods'.
   * The default 'read' setting for a new doc is 'anyone';
   * to change the default 'read' capability to 'loggedin', you'd do:
   */
  $defaults['read'] = 'loggedin';
  return $defaults;
}