> What you wrote is true, but it also seems to me unlikely that the OP is going to set up a sandboxed hermetic build to process a handful of pngs for her zine.

But it's trivial!

Assuming you fix the OP's Makefile (so much for Makefile syntax usability):

     # put into Makefile
     THINGS_TO_CONVERT := $(wildcard *.svg)
     all: $(patsubst %.pdf,%.svg,$(THINGS_TO_CONVERT))
          inkscape $< --export-text-to-path --export-pdf=$@

     # put into default.nix
     with import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/7ad5e816faba3f808e2a8815b14d0f023a4e2160.tar.gz") {};
     stdenv.mkDerivation {
      name = "zine-images";
      src = ./.;
      buildInputs = [ inkscape ];
      installPhase = "mkdir $out && cp *.pdf $out";
    }

Now make sure you have sandbox=true in /etc/nix.conf, run `nix build` in the directory, and boom done: hermetic build of zine images. Good thing too, I got a warning about --export-pdf being deprecated when I ran this. Note that running make or the dependency on make is not explicitly specified, mkDerivation has some basic smarts to figure out from the presence of a Makefile that it should run make.

(Hardcoding the version of nixpkgs directly into the default.nix just for demo purposes, better to use niv or similar to manage a json file with versions for you).