Simply add the buildpack to your Heroku app, e.g.
heroku buildpacks:add -a MY-APP https://github.com/amitree/heroku-buildpack-poppler
To update the debian package, run:
docker build --build-arg version=0.81.0 -t amitree/poppler:0.81.0 .
docker run --rm -v `pwd`:/mnt amitree/poppler:0.81.0 cp /poppler/build/poppler_0.81.0-1_amd64.deb /mnt/