In order to be able to extract or attach additional-data.xml files from or to a pdf file the package ships with the command line tool additional-data-util. See type additional_data_util in your shell for details.

extracting embedded files from a pdf

After installing the additional_data_package, you can extract all embedded files from test.pdf via

$ additional_data_util test.pdf

To embed an additional_data xml file(adm.xml) that corresponds to xml schema (schema.xsd) into test.pdf type

$ additional_data_util test.pdf ad.xml schema.xsd

All 3 files must be located in your current working directory. Otherwise use absolute paths in the call.