PCAF is not a legal requirement in itself, but it is the reference methodological standard for meeting requirements that are. The CSRD requires financial institutions within its scope to publish their scope 3 category 15 (financed emissions) through ESRS E1, and ESRS E1 refers to the PCAF standard for financed emissions. In practice, documenting financed emissions without PCAF is difficult to defend before an auditor today.
Read the source article: An investment fund's GHG emissions: the PCAF method