The Discarded layer and its four sublayers display the objects that were discarded as part of the initial merge process:

• Discarded from <originalfile>.pdf—objects that are unique to the original file
  
   
  
  
• Discarded from <revisedfile>.pdf—objects that are unique to the revised file. Since all objects that are unique to the revised file are preserved by default, this layer is initially empty.
• Discarded from Common—objects that are the same in both files. Since all objects that are the same in both files are preserved by default, this layer is initially empty.
• Discarded Kodak Traps—traps associated with objects that are unique to the original file. If all traps are associated with objects that are the same in both files, no traps are discarded and the Discarded Traps layer is initially empty.