Various types of PDF

Hello,

I am using the latest xmp SDK to write metadata to different file types. Most seem to work as expected, but I have 1.3 and greater pdfs that the SDK fails to write to. I look at the PDF's object structure and see xmp in the file, but the SDK still rejects the file as not supported. Is there some mode I can put it into to write the data no matter what created the PDF?

Thanks

Dean Krueger