tomifocus

Thanks for your hint. I can confirm that after creating the second admin account the Documents menu was appeared. This points to the fact that the missing “Documents” menu issue will probably be caused by changed user roles.
In my case I faced this issue after several plugins were installed for my WordPress site.
So probably one of these plugins overwrote/changed the admin user roles under wp_usermeta database table. And WP Document Revisions plugin requires the default administrator user roles to display “Documents” menu in WordPress dashboard menu.
Therefore I opened wp_usermeta database table, clicked on edit button at wp_capabilities of admin user and made a copy about the meta_value. Then overwrote the wp_capabilities meta_value with the default admin value: a:1:{s:13:”administrator”;b:1;}.
Then the issue was resolved at the original admin user as well.
Always make a backup before the manual database table modification that you can restore for the case if you would make any mistake. And after the modification test your wordpress site and the used plugins to know everything is working properly.