Reply To: How to Permanently Delete Cropped Data in a PDF

I finally found it! Sharing in case anyone else needs to do so.
For Acrobat Pro DC version:
Crop your document to remove crop marks, registration marks, anything else outside the image area.
Choose Tools > Redact, and then select Remove Hidden Information.
Acrobat searches for any hidden info, and lists it to the left of the main window.
Make sure check marks are in boxes for anything you want to remove, and then click on remove.
File > Save.
Registration and crop marks are now gone, and the file does not throw an error of finding a four color black!!