Are only regular employees of a securities company, regardless of their position, allowed to store files in the company? Or is it only possible for those within the staff?

This should vary according to the nature of the securities company. Generally, the business department of a joint-stock securities company does not have personnel custody rights. That is, the files of all personnel who are not at the company headquarters, including regular employees, are Hosted to the local talent exchange center; for state-owned securities companies, it is possible that regular employees store the files in the company and other personnel manage them themselves.