Previews (to customers) only show what's inside the ‘Trim Box’.

When Orders are made, Admin will receive the full PDF.

Whats the trim box? i hear you ask. Lets start with a full PDF. Here is one we created that has all sort of stuff around the edge, including crop marks as marked by the yellow arrows.

Now go to Set Page Boxes (Acrobat Pro)

You can see here that I've set the trim box to 'exclude' all the printer marks.

If this PDF is now uploaded in the Page Background for an editable product, the customer will only ever preview whats inside the trim box.

Heres a video which shows the process
​