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 
exiting DPP.
 On 32-bit OSs, only up to 1000 images can be displayed per 
collection folder. Starting with the 1001st image, images are handled 
in the same way as non-supported images. Try to maintain 1000 
images or less per folder.
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, right-clicking 
with the mouse, 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 when you right-click with the 
mouse. 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.