Backward compatibility problem...acrobat 8.0 vs reader 6.0

Question

Not sure if this is the right forum, but will start here & move if necessary.
We have been using Acrobat 8.0 for 2-3 years & have never had a problem 'til now.  We will be creating a series of documents 1-10 pages long, with sound clips in them & anticipate that some of the systems viewing the documents may be as dated as W98, so we set the PDF configuration to be backward compatible to reader 6.0.
Earlier today I downloaded a copy of reader 6.0, just to make sure all worked...it didn't.  Instead, I get "this file appears to use a new format that this version of acrobat does not support."
The document I used to test was, again, creadted w/acrobat 8.0, set for backward compatibility to reader 6.0.  The document was 4 pages long with 4 color photographs & 2 .mp3 sound clips embedded.
Anybody have any ideas where the problem is?  The test file reads OK on current version readers, so does Acrobat 8.0 not really generate backward compatible documents?

Answer 1

Follow Bernd's suggestion. You probably added something to the file after creation (like the sound clips) and the method you used is not AA6 compatible. Saving the file (or save as) does not preserve the version compatibility, but changes it to AA8. To maintain backward compatibile versions, you have to be sure you do not add AA8 only features and use Reduce File Size or PDF Optimize to save the file as an AA6 compatibile file.
Typically AA6 will open an AA8 file, but will ignore any new feature. You may have added something it can not handle. I don't recall if AA6 could handle embedded mp3 files.