The main purpose of the stage 1 audit is to verify whether your environmental management system is designed and compliant with the requirements of the standard. Anything can be audited in terms of documentation. Stage 1 audits are not for auditing implementation. So, do not expect stage 1 audit to go audit operations, for example.
Documents to be reviewed during this stage of the audit are all the documents that belong to the scope of your management system, this includes documents required by the standard itself and the ones that the organization determined as necessary for effective maintenance of the management system.