When you compare two PDF files for the purpose of highlighting the object differences between them, PDF Compare creates a temporary comparison file and opens it in Acrobat.
The following figure shows a sample comparison file highlighting object differences.
This comparison file includes four layers:
- Objects that are unique to the original PDF file
- Objects that are unique to the revised PDF file
- Objects that are common to both files
- Objects that are different between the two files, highlighted in the highlight color that you specified in the Prinergy Compare Documents dialog box
The Layers tab to the left of the comparison file lists each of these four layers.
By default, the two unique object layers (Unique to <file>) and the layer that highlights object differences (Object Differences) are displayed, while the common objects layer (Common) is hidden. However, you can switch the layers on and off by clicking the eye 
icon next to each layer. A layer with an eye next to it is displayed; a layer with no eye is hidden.
By switching layers on and off, you can make unique and common objects visible and easier to see. For example, the figure that follows shows a comparison file for the PDF files K_Original and K_Revision. While the text Prepress solutions for packaging is common to both files, because it is white, it is only visible when you display both the Common layer and one or both of the Unique layers.
Differences between the two files can include colors, objects and object positions, fonts, overprint states, and anything else that would create a visible difference.
To see only objects that are different between the two files, hide the first three layers and display only the Object Differences layer.
