More about read pdb
here.
Q: How do I save the entire loaded molecule to a new PDB file?
A:
write pdb a_ "whole_object.pdb"
More about write pdb
here.
Q: How do I save just a specific chain or selection to a PDB file?
A:
write pdb a_e "chain_e.pdb" – Save chain E
write pdb a_e,we "chain_e_and_water.pdb" – Save chain E and water
More about selections in the ICM command language
here.