how do i get the coordinates of atoms from the output of the 'vtkPDBReader' object?

the vtkPDBReader object can read the PDB file. how could it get the information of molecule of protein and amino acid , the coordinates of the atom, etc? Thanks for your reply!

The code is here: https://gitlab.kitware.com/vtk/vtk/-/blob/master/IO/Chemistry/vtkPDBReader.cxx?ref_type=heads