Smartcard / USB tokens provide a safe physical support to store certificate private keys required to apply digital signatures on a document. They add an additional layer of protection to the signing process, as not only do users need the password but also the physical hardware token to access and use their certificate. It is the technology used for instance in DOD CAC Certificates.
PDF Studio has support for the Windows certificate store. Windows users are able to sign using smart cards / USB/ hardware tokens through their operating system store.
MacOS has a digital certificate store but there is an Apple bug that prevents PDF Studio from accessing token certificates.
PDF Studio allows Mac users to sign using smart-card tokens by allowing them to specify the link to a PKCS11 token configuration file. Please read this entry in our knowledge base:
How to setup USB Smart Card Hardware PKCS11 signing on Mac
Linux / Unix
Linux does not have a digital certificate store / framework that abstracts the complexity of accessing certificates.
PDF Studio allows Linux users to sign using smart-card token by allowing them to specify the link to a PKCS11 token configuration file. Please read this entry in our knowledge base:
How to setup USB Smart Card Hardware PKCS11 signing on Linux