For anyone who finds this little thread in 2020 or beyond, these printers can only print PDFs from USB if they have created the PDFs themselves. The feature I think was intended as a kind of "copy to storage" and "print from storage" thing for customers that do a lot of document duplication. This is noted in the quick reference booklet if you still have have it.

If you can't fit the printer next to the computer that needs it, your best bet is probably using the ethernet connection on it - either directly into a router or into a live wallplate with an ethernet port.

If you need to go the ethernet route, use the menu system on the printer to print out a report of its network configuration after it's plugged into ethernet - this will give you its IP address and Hostname. In Win 10 under Settings>Devices and Printers, add a printer, choose "My device is not listed" or equivalent, choose "Setup with Hostname/IP" or equivalent and then type in your printer's IP to have Windows locate it, the
"port information" should just fill in as you type your IP, and it's fine like that.

I've confirmed that Windows Update has the right drivers for these old printers - it's probably under manufacturer "DELL", not (Dell Inc. or the other one). It will take a few minutes for the list to update, btw.