Had the same problem, seems to be a new table that comes with 4.0.4 but the upgrade script does not create it. I used PHPMYADMIN and created the table using the following code (where <table prefix> is the prefix used by your Joomla installation :

CREATE TABLE IF NOT EXISTS `<table prefix>_joomdoc_user` (
`user_id` int(11) unsigned NOT NULL,
`document_id` int(11) unsigned NOT NULL,
`notifications` tinyint(1) NOT NULL,
UNIQUE KEY `user_id_document_id` (`user_id`,`document_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;