A version of arminstraub's krop PDF cropper, patched to use PyPDF4 instead of PyPDF2, and with some minor fixes added.
It's packaged up as a UPX-compressed executable using PyInstaller, and a quick-and-dirty Debian package is provided.
Because PyPDF2 is apparently not being maintained, PyPDF4 is only sporadically maintained, and both contain some known bugs.
Docker on Ubuntu or similar; make.
$ git clone https://github.com/phlummox/krop-patched.git
$ cd krop-patched
$ make copy
$ sudo dpkg --install krop-0.5.1.deb