putting a file reference at the bottom of a document

I want to show a file name at the bottom of the document

You tagged your question common. This means it applies to Writer, Calc, Impress, Draw, Base and Math. I doubt you practice all components. So, read these guidelines, edit your question (don’t use an answer) and its tag. Provide more details and mention OS and LO version.

Also read this tutorial and this tutorial.

Hi Flockie
I’m picking you mean for Writer as you said document and that it is common in your workflow. Click where you want the file name. In the menu select Insert | Field | More Fields… or just CTRL+F2 (assuming your F keys haven’t been allocated to something else). Select the Document tab in the window that appears. Click on File Name from the list and you have a choice of 4 options for how much you want showing.
If you haven’t saved your file you will just see a narrow grey rectangle, once you save your file it will show as much of the file name and path as you chose.