I guess user x has access to company A and B , set as the accessible companies on the users settings. But when you logged in , in a multiple company setup, you get a current company where you are working in, you can change this in the users preference or use this handy company switching module https://www.odoo.com/apps/modules/7.0/web_easy_switch_company/

But when you need to print something from B but you are in A, you need to change company.