Work inside your systems
The safest model is for offshore professionals to work inside your firm's own audit software, document management and practice systems, with access you grant and can revoke. Client files stay in your environment.
Questions to ask any provider
Are staff bound by confidentiality agreements? Is work performed in a controlled office environment? How are devices, logins and access managed? How are staff onboarded to your firm's data handling policies? What happens when someone leaves?
Align with your obligations
Your firm should confirm the arrangement fits its professional obligations, privacy requirements and any client contractual terms. Document the controls so they can be evidenced during quality reviews.