The latest upgrades in PDF technology always fix old problems and create new problems with their new features. One issue showing up in new PDF workflows is a problem with a PDF feature called “Optional Content”.
Optional content is discussed in section 4.10 of the PDF Reference Manual, and refers to sections of content in a PDF document that can be selectively viewed or hidden by document authors or consumers. This capability is useful in items such as CAD drawings, layered artwork, maps and multi-language documents.
Container tags in a PDF document can be seen in Acrobat 8 by viewing Navigators-> Content. The Content Navigator will show you a breakdown of pages and lists all of the pieces of the PDF by page. Pop the arrows down and items such as images, text blocks, and other elements show up. Items can also be grouped together in a package or container and will be identified by a container tag.
The Container tag “OC” for optional content has been causing trouble with many rips and is difficult to catch when you don’t know where to look. Items on a page with an “OC” tag in the PDF may print once but can completely disappear on the second ripping. PDF items that are tagged “OC” may or may not print. Do you see the problems that this can cause?
So how do you catch this problem before it goes to the rip? It’s certainly not an easy solution.
Acrobat preflight does not have any choices when making a profile to match a container tag to “OC”
Third Party Preflight software checks for layers but not “OC” Container tag specifically
You can visually scan the content navigator, but in a multi page PDF you must manually pop down all of the pages and scan the list for an OC Container
When you find an item that has the OC Container tag you must select it with the touch up object tool in Acrobat 8. Control Click and select properties from the contextual menu. Change the tag to another item in the list such as “Part”. You can also change it right in the Content Navigator list by selecting it and showing its properties.
Here are some ways that this tag can be added to a PDF without your knowledge:
‚Ä¢ Colour correcting an image in a PDF using Photoshop (version CS only). Newer versions of Photoshop do not cause this to happen
‚Ä¢ Making changes to a PDF using the touch up object tool and editing in Illustrator CS3. Illustrator CS2 does not cause this problem.
It is safe to say that when you make any changes (such as those listed above) to your file you should change the container tag from “OC” to “Part” in the properties of the object or in the Content Navigator. It would be a good habit to inspect the Content Navigator after any changes have been made to a PDF just to be sure.
I haven’t found a way to digitally preflight for this specific issue. By the time this article is published, I am sure that patches will be created for rips and updates will be made for third party preflight software. One thing is for sure, when this issue is fixed, a new issue will take its place.
We get comfortable with our hardware, and when we have a short time where software has the kinks worked out, we stop checking our work so diligently. Change happens, so we must rely on the one thing that should not change: our Quality Control systems that compare what is signed off by the customer to what comes off the press. For the best quality, we need to stay one step ahead of our equipment.