I still have a thermal Panasonic fax in my office, and I use it as a very nice phone with a very good handsfree function, and it works well for this. I occasionally send a fax with it, at least i did send 2(?) this year. I also have a spare one, just in case it breaks. They were going to be thrown away, but I plugged one in and it was better than the phone I had.
As to trailing edge OS's I still have a PC around running Win98, and connected to the network as well, though remoting to it is not good as it tends to crash the desktop on closing the remote VNC connection. Still in use running a phone software as a single app, and I have a backup machine for it as well. Some spare 4G drives as well.
With printing to PDF, it is pretty much a free part of CUPS, and works well.