As with object difference highlighting, when you compare two PDF files to highlight the ink differences between them, PDF Compare creates a temporary comparison file and opens it in Adobe Acrobat.
The comparison file includes layers for objects that are unique to the original PDF file, unique to the revised PDF file, and common to both files. However, instead of a layer highlighting the object differences between the two files, the fourth layer (and its associated sublayers) highlights ink differences—changes to color separations—between the two files.
The following figure shows a sample comparison file highlighting ink differences:
By default, the two unique object layers (Unique to <file>) and the layer that highlights ink differences (Ink Differences) are displayed, while the common objects layer (Common) is hidden.
You can switch the layers on and off by clicking the eye 
icon next to each layer.
The Ink Differences layer has one or more associated sublayers, each of which represent a color separation that has changed between the original PDF file and the revised PDF file. The number next to each separation name indicates the percentage of pixels that changed for that separation. If a color separation is not listed, it did not change between the original and revised PDF.
Tip: The Ink Differences layer lists only separations that have changed between PDF files. However, you can click the Information icon in the upper-left corner of the comparison file to display a dialog box containing more details about each of the PDF files, including those separations that did not change between the original and revised PDF. Such separations are listed with a Difference of Identical.
A separation layer with a change percentage of 100 percent usually indicates that the separation was contained in the original PDF file but does not exist in the revised PDF file, or vice versa. Alternatively, a change percentage of 100 percent could indicate that the separation exists in both PDF files, but is blank in one of the PDF files.
You can hide and display individual separation layers only when the main Ink Differences layer is displayed (switched on).
When the Ink Differences layer is displayed, separation differences between PDF files are highlighted in the highlight color that you specified in the Prinergy Compare Documents dialog box (rather than in the actual color of the separation). For example, in the figure that shows a sample comparison file highlighting ink differences, those objects unique to each PDF file are displayed. Changes to the color separation PANTONE 376 C are also displayed, highlighted in red.
Displaying only the Ink Differences layer and its sublayers is useful when you need to remake plates and want to know which separations have changed so that you can remake plates only for those separations.
See Also