I am having troubles exporting a PDF to PDF/A-1b using Adobe Acrobat X Pro. I've already asked the same question at the official Adobe forum, but got no response. I hope somebody here could explain what is going on...
When I try to export a PDF/A-1b from a source PDF that also contains metadata from http://purl.org/dc/terms/ namespace, such as,
<rdf:Description rdf:about="" xmlns:dcterms="http://purl.org/dc/terms/"> <dcterms:alternative>Alternative Title</dcterms:alternative> </rdf:Description>
I get an error saying that: "XMP property neither predefined nor defined in extension schema" although the root RDF element includes
xmlns:dcterms = "http://purl.org/dc/terms/". At the moment I delete all dcterms elements the document exports correctly.