PDF versions are not the same as the versions of Acrobat. See here a
specification of the various PDF versions:
Basically, unless the file contains new features which are not compatible
with older versions, you can save a PDF as an earlier version using Acrobat.
We only use Adobe for creating pdf files so I'm certain that if I can get a converter for Adobe, I'll be able to get these documents indexed in our KM system.
Acrobat Pro (8, 9, X) has Preflight profiles that support saving PDF to earlier versions.
As well there is the PDF Optimizer.
So, if you have Acrobat Pro you need nothng else.