You may search on ProtCID by PDB ID (e.g. 3Q4Z), Pfam ID (e.g. Pkinase_Tyr) or Pfam Accession Code (e.g. PF07714),
a pair of Pfams (e.g. IMPDH and CBS), a list of UniProt IDs, and one or two sequences.
All searches lead to chain/domain common interfaces.
You may also use the navigation bar on left of the page to guide your search.