If you make a pdf from word (with generate tags on) and then run the auto wizard for accessibility in pdf it will generate the footnote tag when it auto tags.
I'm having trouble finding documentation on how the <footnote> tag is used and would like to know more.

First, the PDF/UA-1 standards do not have a <Footnote> tag, so if any program is using it, that is an error.
You can discover all of the allowable tags in a PDF by looking at the Properties/Tag of an existing tag:
- Open a PDF.
- Select a Tag.
- Right-Click and select Properties.
- The drop-down Type menu lists all of the available tags.

Note that their names are fully spelled out and don't use the required tag name: example, <H1> is shown in the drop-down as Heading 1, but Acrobat puts the correctly spelled tag in the tree.
Now, back to Word...
- Which version of Word are you using?
You can find this under File / Account (see screen capture below) - Mac or PC?
- And how are you exporting/converting the PDF?
With the Acrobat PDFMaker plug-in (the Acrobat Ribbon) or via MS's File / Save As / PDF utility?
