For that I believe you'd need the parallel interface, which allows transfers between PCs and the Portfolio, first item on page
here.
I found mine on eBay a while back, with box and software, for well under the $50 that Best wants. I haven't done anything with it yet, but someday...
Also, you may have some problems with the software side on the PC, as the software that comes with the Portfolio is ancient. (MS-DOS 3.3 days, anybody?) There's more info
here. Apparently USB-to-parallel adapters don't work, so you'll need access to an older PC with those ports on-board. As for the OS side, you could try setting up a virtual DOS machine with
VirtualBox, which is free, but requires some futzing around and also requires a set of MS-DOS 3.3 software to install on the VM. I tried using VirtualBox under XP to allow communication with an old home controller over serial but only got it to work once. My solution was to make a 40MB partition on the hard drive, load DOS 3.3 on it, then use a boot manager to allow me to boot from it. That works well.
As you can tell, operations like this require knowledge about the ancient OSes from computing's dark days...or knowing someone who knows that stuff.