Canon EOS-1D X Manual (en)

Check the displayed images.
Edit the images.
Edit the displayed images.
Displayed images are retained in the collection folders even after 
quitting DPP.
Removing selected images
Select images in a collection folder, select images, and select 
[Remove from collection] in the [File] menu. (You can also remove 
images from a collection folder by selecting the images, holding down 
the <control> key, and selecting [Remove from collection] from the 
menu that appears.) Note that even if you remove an image from a 
collection folder, the original image remains unaffected.
Removing all images
Select [Clear collection] in the [File] menu. Note that even if you 
remove all images from a collection folder, the original images remain 
Deleting a collection folder
Select a collection folder in the collection area, then select [Delete 
collection] from the menu that appears while holding down the 
<control> key. Note that if you delete a collection folder, the original 
images remain unaffected.
To remove images from collection folders
Modifications to the image are applied to the original image
Modifications made to images in a collection folder are all applied to 
the original image.