Support for adding custom document meta data to existing PDF documents

The similar methods are available from com.pd4ml.PD4ML (v4 API) directly. There are setAuthorName(), setDocumentTitle() and addMetadata() for arbitrary meta data settings.

https://pd4ml.tech/javadoc/com/pd4ml/PD4ML.html#addMetadata-java.lang.String-java.lang.String-boolean-

Document creator property can be overridden only via dedicated environment variable.