Depends on your underlying storage. PVE usually uses LVs with LVM/LVM-Thin or zvols with ZFS. Both are blockdevices so there are no files. You could mount the blockdevices on the host (make sure the VM is stopped as long as you mount it, or otherwise you will corrupt the VMs data!!) and then copy stuff to/from the mountpoint.
But would be easier to just SSH into a running VM to copy stuff, as long as your VM is still able to boot.