Here is a list of all documented files with brief descriptions:

pkcs11-helper-1.0
pkcs11.h
pkcs11h-certificate.h	Pkcs11-helper certificate functions
pkcs11h-core.h	Pkcs11-helper core
pkcs11h-data.h	Pkcs11-helper data object support
pkcs11h-def.h	Pkcs11-helper core definitions
pkcs11h-engines.h	Pkcs11-helper engines definitions
pkcs11h-openssl.h	Pkcs11-helper OpenSSL interface
pkcs11h-token.h	Pkcs11-helper token interface
pkcs11h-version.h	Pkcs11-helper core