[PDFdev] Acrobat 5 not upwardly compatible with Acrobat 4?

[Antony James Clark]

Why can I not print duplex (two-sided) with Acrobat 5 while I can with Acrobat 4? Also I cannot replace pages using Acrobat 5. These PDF files are generated using a program I wrote some time ago, and I suspect something is broken, but where? If one of you could point me in the right direction I'd be most grateful. Antony Clark