Plugin to manually add users

Hi. I’m trying to start a site where my company can manually add users (employees). The general public can not register. “Anyone can Register” is unchecked.

I need to add/modify “new-user.php” to add more fields, and make all fields non-modifiable by the users (employees) in their profiles.

I’ve been unable to find such a beast in the Plugins section, and my knowledge of coding is not great.

This could be a very useful plugin for many people.