Ok, I'm no expert on this issue, but according to wikipedia PDF/X-1a:2001 is based on PDF 1.3 with the addition of "blind exhange and Spot colours."...
Just to get you through to the end of the week, you might be able point your sources file to http://old-releases.ubuntu.com/ where the lucid packages...
That would be because support for 10.04 (lucid) on the Desktop ended last week on the 9th. There won't be any software or security updates coming for...