Converting between '.crd' and '.pdb'

You can actually convert between '.xyz', '.pdb' and '.crd' formats using awk and other shell commands. There is more info on the conversion between different data file formats page. Another way of doing it is using CHARMM to read in your structure in one format and then specifying that you would like to save it in a different format. The advantage of using CHARMM for this is that you know the output structure will be readable by CHARMM!