As with any major upgrade, the release of the Acrobat 6.0 line has meant that many PDF users are dealing with compatibility issues straddling multiple versions of our favorite file format. One such issue has been that when people attempt to open Acrobat 6.0-created PDF files in previous versions of Acrobat such as 5.x. In this situation, Acrobat will spit out the standard warning message (below).
A bit of a problem if you want the process to be seamless, eh? Well, here's the reason: by default, Acrobat will save output PDFs as the latest version, in this case, PDF 1.5. Acrobat 5.x will then detect that something's up, and spawn the aforementioned warning. The good news is that the problem is easily fixed as long as you are not trying to use any special features unique to PDF 1.5.
Both Acrobat 6.0 Standard and Professional include a menu item (File, Reduce File Size) for reducing the file size of the current document. Another benefit of the tool is that you will also have the chance to set the Acrobat version compatibility. After that, Bob's your uncle: Acrobat 6.0 will make its best effort to compress your document using the available technologies for the appropriate version. For example, the newest version of Acrobat includes support for JBIG2 and JPEG2000 image compression technologies, but if you choose a previous version, these will not be used.
The PDF Optimizer
As I mentioned, this tool is available from both the Standard AND Professional versions of Acrobat, but Pro users get even more power over the process, via the PDF Optimizer.
The PDF Optimizer expands on Acrobat 5's PDF Consultant -- which allowed users to examine the space usage of different elements of a PDF file and then remove them from the PDF to reduce its size. Like PDF Consultant, however, PDF Optimizer can also be used in Batch Sequences.
PDF Optimizer extends the functionality of the PDF Consultant so that in essence, the tool becomes more like a 'redistiller' or 'refryer' (the term used by many in the PDF community for redistilling a PDF). So, like Acrobat Distiller, you have options to downsample images and un/embed fonts as well as remove document elements, including fonts, comments, form actions, document structure, hidden layer content and the like.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.