bp_document_update_activity_document_meta( $content,  $user_id,  $activity_id )

function bp_document_update_activity_document_meta( $content, $user_id, $activity_id ) {

	if ( ! isset( $_POST['document'] ) || empty( $_POST['document'] ) ) {
		return false;
	}

	$_POST['documents']          = $_POST['document'];
	$_POST['bp_activity_update'] = true;
	$_POST['bp_activity_id']     = $activity_id;

	// Update activity comment attached document privacy with parent one.
	if ( bp_is_active( 'activity' ) && ! empty( $activity_id ) && isset( $_POST['action'] ) && $_POST['action'] === 'new_activity_comment' ) {
		$parent_activity = new BP_Activity_Activity( $activity_id );
		if ( $parent_activity->component === 'groups' ) {
			$_POST['privacy'] = 'grouponly';
		} elseif ( ! empty( $parent_activity->privacy ) ) {
			$_POST['privacy'] = $parent_activity->privacy;
		}
	}

	remove_action( 'bp_activity_posted_update', 'bp_document_update_activity_document_meta', 10, 3 );
	remove_action( 'bp_groups_posted_update', 'bp_document_groups_activity_update_document_meta', 10, 4 );
	remove_action( 'bp_activity_comment_posted', 'bp_document_activity_comments_update_document_meta', 10, 3 );
	remove_action( 'bp_activity_comment_posted_notification_skipped', 'bp_document_activity_comments_update_document_meta', 10, 3 );

	$document_ids = bp_document_add_handler();

	add_action( 'bp_activity_posted_update', 'bp_document_update_activity_document_meta', 10, 3 );
	add_action( 'bp_groups_posted_update', 'bp_document_groups_activity_update_document_meta', 10, 4 );
	add_action( 'bp_activity_comment_posted', 'bp_document_activity_comments_update_document_meta', 10, 3 );
	add_action( 'bp_activity_comment_posted_notification_skipped', 'bp_document_activity_comments_update_document_meta', 10, 3 );

	// save document meta for activity.
	if ( ! empty( $activity_id ) ) {
		bp_activity_update_meta( $activity_id, 'bp_document_ids', implode( ',', $document_ids ) );
	}
}