Briss - a great tool to split 2 page scan to 1 page

 https://sourceforge.net/projects/briss/

Require JAVA

This project aims to offer a simple cross-platform application for cropping PDF files. A simple user interface lets you define exactly the crop-region by fitting a rectangle on the visually overlaid pages.

Features

• Crop PDFs GUI based
• Crop different regions into separate pages
• Crop multi column/pages