Converter between PDB or mmCIF and MMTF
I wrote a very quick and dirty script to handle conversion between file types using BioJava.

https://github.com/eedlund/Utils/tree/master/BioUtils

Download the jar file here

To run: java -jar BioUtils.jar $FILE $TYPE

where \$FILE is a PDB or mmCIF file you'd like to convert and \$TYPE is the format of the output file [PDB, CIF, MMTF].