PDF Forward Compatibility Issues
A couple of interesting articles on pdfzone.com highlight the perils of digital preservation.
The two articles (Adobe Battles Backward-Compatibility Woes and Some Backward-Compatibility Problems (But Not All) Have a Happy Ending) show how hard it is to preserve any complex digital document.
Every bug and idiosyncracy must be kept exactly as is. Any deviation is bound to break something somewhere. It also points out the need to have a "validator" that can detect invalid or corrupt files. My understanding is that there will be something like this for PDF/A.
Virtualization, which simply preserves the old software environment "as-is" is one way to try to work around this.
Via Gary McGath's File Formats Blog
File Formats: PDF