Viewing rights with Copilot Pro

KLM16 

I understand you are talking about adding Copilot to your work environment to the users using their Entra ID and password. If that's the case, then you check the license "Copilot for Microsoft 365" license which is specific for Work environment.

Copilot Pro is ONLY for personal account users like outlook.com or hotmail.com which cannot incorporate with your work data.

Coming to Copilot for Microsoft 365 security concerns, It is already built on your existing M365 environment Security, Privacy and Compliance controls. With that being said, you have do a Access review in your SharePoint sites and files and add/modify/remove access as per the requirement. Use the least privilege method. Do not assign license to your users until you prepare your environment.

https://blogs.microsoft.com/blog/2024/01/15/bringing-the-full-power-of-copilot-to-more-people-and-businesses/
Copilot Pro (Personal) - https://www.microsoft.com/en-us/store/b/copilotpro
Copilot for Microsoft 365 (Work) - https://www.microsoft.com/en-us/microsoft-365/business/copilot-for-microsoft-365?SilentAuth=1&wa=wsignin1.0&rtc=1