dir2pdf is a tool that combines plain text files in a single pdf file. With ingredients section, you can easily switch files. I needed this program for reading source codes of any project on my kindle easily.
PyPDF2
$ git clone https://github.com/aliagdeniz/dir2pdf
$ cd dir2pdf
$ python dir2pdf.py
$ python dir2pdf.py <directory>
GNU GPLv3
Issue it here: https://github.com/aliagdeniz/dir2pdf/issues