Updating PDF attributes

The PDFDocument class makes updating metadata attributes simple but appears to:

1. Disallow arbitrary values for the /Producer attribute - the wite action substitutes an Apple string as the producer
2. Offer no choice over the PDF version or the write format - it's 1.4, and compressed regardless of the original PDF format

Am I missing something simple in the PDFDocument class that will over-ride this behaviour?

Is the PDFDocument structure archive conformant and, if so, to what level?

Is it necessary to deal directly with CGPDFDocument to overcome these limitations?

cheers,

david