问题
I have an XML document which is already Xades signed. Now I want to counter sign this signature. How can I do this with Xades4j? I have searched the documentation but there is only example how to sign and countersign together.
回答1:
You can use a format extender directly to add new unsigned properties to an existing signature.
来源：https://stackoverflow.com/questions/14696429/xades-countersign-document