Saving a permanently cropped copy of a file
overflow button and tap Save a Copy, then tap Permanently Cropped Copy from the sub-menu. 
2. If the file is not yet cropped, you will need to crop it first. The permanently cropped copy will show up as cropped in any PDF viewer.
See Also:
Cropping Pages
Saving a copy of a file
Saving a flattened copy of a file
Saving a password protected copy of a file
Saving a reduced file size copy of a file