This is not a comprehensive answer to your query, but it's a start
A PVR is a Freeview set-top box with a hard drive in it. It would replace a set-top box, and it can record programmes via the Freeview signal onto its hard drive. New PVRs have 2 tuners in them so that you can record from one channel while you watch another, or record 2 channels at the same time and watch something you've already recorded. It cannot record from any source besides the Freeview signal. If it has a USB socket, you can connect it to your PC's USB and transfer files - either upgrades from your PC to the PVR, or recordings from the PVR to your PC.
If you want to archive something permanently onto a DVDR, you could simply connect the DVDR to the secondary SCART socket on the PVR, play the programme on the PVR and set the DVDR to record from the SCART. There are different ways of connecting up, others will advise you better than I (bit muddle-headed

).
clemenzina