Wednesday, December 22, 2004
PDF cross-reference stream
Quietly introduced in PDF 1.5 is a change which can make newer PDF's incompatible with older readers. An essential part of a PDF document is the cross-reference table. Starting in PDF 1.5, this can be replaced with a cross-reference stream, as described in Section 3.4.7 of the Adobe PDF reference. Readers that aren't cognizant of this change will be unable to make sense of documents that take advantage of it. Acrobat 6 deals with this change, while earlier versions don't. (JHOVE currently doesn't recognize cross-reference streams, but this will be fixed in the not too distant future.)
In particular, Adobe's downloadable PDF 1.6 specification contains a cross-reference stream, so this suggests we'll be seeing more PDF's that use the new format in the future.
