To cite ppmf in publications use:

  Christopher T. Kenny (2021). ppmf: Read Census Privacy Protected
  Microdata Files. URL https://christopherkenny.github.io/ppmf.

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {{ppmf}: ppmf: Read Census Privacy Protected Microdata Files},
    author = {Christopher T. Kenny},
    url = {https://christophertkenny.com/ppmf/},
  }