SharePoint Foundation 2013 - Document ID (custom)

Hello;

Its my understanding that SharePoint 2013 Foundation does NOT include SharePoint's Out-of-the-Box Document ID functionality.  Within a Foundation site, I'm looking to implement a rudimentary Document ID-like functionality using existing (or developed) SharePoint functionality.

This doesn't need to be as robust and customizable as SharePoint's own Document ID functionality.  Really all I need is a unique ID (can be numeric, alphanumeric, doesn't matter) applied to or displayed for each document.  My only requirements:

1. The new "Document ID" field must be unique for each doc.
2. Users cannot change the "Document ID" field.

And--it only needs to apply to one Document Library (not the entire site).  I'm thinking the best place to start is creating a new column that's a Calculated field. It could be something as simple as a calculated field that takes the created date/time and adds some other random or unique value to come up with a random number or ID.

In fact, I tried a calculated field that was just simply:   =[ID] (hoping that every doc in a Doc Lib had some internal ID like any other item in a list), which would have worked, but new files I create/add now just show a "0" for this new field.

There must be SOME way to just simply assign a unique value to each doc.  Ideas?