What is the best way to convert multi-column PDF file into readable format in a 6 inch display devices like kindle?
Also check out k2pdfopt by Willus.
I found PaperCrop a very useful and powerful tool. It is free and highly customizable so you can either relay to automatic detection of columns and sections by program or customize each page format.
I have created a python code for this purpose. It solves my problem and hope it will be helpful for others.
Background : I had 2 sided pdf document which I had to zoom for clarity. I decide to create this python application which will break 2 column page into 4 pages.
If you don't understand then : just run python3 main.py, and see if it is what you are looking into.
I found this small Java utility .
Very simple to setup and quick to use and gives a pretty nice result on my Kindle.