When creating Section 508 compliant PDFs from InDesign source documents, I occasionally end up with PDFs sized wildly out of proportion to what their actual size should be. This happened recently when I exported a tagged PDF from an InDesign file received from a third party. While I was trying to figure out what had bloated the file and how to reduce its size, a colleague referred me to an article on document bloat by David Blatner on the blog, InDesignSecrets.com. The article is well worth reading if you export PDF files from InDesign. The primary take-away for me from this article was the use of the PDF Optimizer to determine the source of the bloat and how to reduce it. The PDF Optimizer is found by selecting Save As > Optimized PDF from the File menu in Acrobat Pro X or selecting PDF Optimizer… found under the Advanced menu in Acrobat Pro 9.
On the resulting PDF Optimizer dialog box, you will find a button labeled “Audit space usage…” This dialog will provide you with a list of space usage within the PDF file. The example shown below shows that Document Overhead consumes 3.5 GB, almost 93 percent of the total file space. I have no idea what document overhead is, but it clearly is the culprit in bloating up this PDF.
To reduce the gross amount of document overhead, select “Discard User Data” from the PDF Optimizer and check “Discard document information and metadata” as shown below. When you run this function, you will lose your metadata, so make sure you have it captured so you can reenter it.
In the case of the file shown, this one fix reduced the file size from 3.8 MB down to 279 KB.
The standard methods of reducing bloat in the InDesign document itself (5.6 MB in this case) were not effective in preventing PDF bloat. The standard techniques of doing a periodic Save As… or exporting the file as an InDesign Markup (IDML) document and reimporting it into InDesign did nothing to reduce bloat. Only using the “Discard document information and metadata” fully reduced the bloat for this file.
The full article can be found on the InDesign Secrets site at http://indesignsecrets.com/document-overhead-in-indesigns-pdf-can-be-huuuuuuge.php