PDF 1.4 files can contain a transparency feature that cannot be described in native form in PostScript or in PDF 1.3. Transparency can be created in newer versions of Illustrator software 9 and 10, and InDesign 2 software. For transparency to be represented in PostScript and PDF 1.3 files, it must be flattened. That is, two transparent PDF 1.4 objects are converted to three opaque PostScript or PDF 1.3 objects, the third object being the PostScript representation of the overlap between the two PDF 1.4 objects.
You can save PDF 1.4 transparency for submission as:

• An EPS element placed within another application. The EPS must be flattened at the highest quality setting before it is submitted for refining.
• A PostScript or PDF 1.3 page. Again, the file with transparency must be flattened at the highest quality setting before it is submitted for refining.
• A PDF 1.4 page. In this case, the system detects and automatically flattens the page using the highest quality setting.

Note: If you use a low quality setting when flattening files with transparency, text may become rasterized and result in fuzzy edges when processed. For the latest recommendations on flattening outside of the system, see http://www.adobe.com.