I use the Mac OS X PDF viewer as an example, but this really applies to any circumstance where a PDF is generated in a newer version of Acrobat (or other PDF generator), then opened in an older version.
In one very common case, newer versions of PDF readers have much better support for transparent images. If you are using transparent images in your PDF, and want to support older readers (such as the Mac OS X reader), you may want to do one of three things:
- Export your PDF as an Optimized PDF, and choose an older compatibility setting (Acrobat 5, for example)
- Don't use transparent images
- Offer two versions of your PDF (one optimized for older readers, and one for newer)