International Tables for Crystallography, Volume G: Definition and exchange of crystallographic data (2006). Hall, S. R., & McMahon, B. (Eds.). DOI: 10.1107/97809553602060000107.
This is the canonical reference for CIF. A revised edition is currently being prepared (2026). Volume G includes a chapter on powder diffraction and another on pdCIF. If your library does not have a physical copy of this, they may offer on-line access.
“Use of CIF for powder diffraction data,” Chapter 4.10. (2019) B. H. Toby, in International Tables for Crystallography, Volume H: Powder Diffraction, edited by C. J. Gilmore, J. A. Kaduk, and H. Schenk, DOI: 10.1107/97809553602060000889
A shorter and less comprehensive introduction to pdCIF is available in this volume. Again, if your library does not have a physical copy of this, they may offer on-line access.