Do you have to inform PIP when you start receiving your state pension

Hi @mylo2018 and welcome to the community. I can't answer your specific question as I'm not an authority on PIP. I did find this post, however, by member @Username_removed from which I'm quoting: "PIP has no impact on state retirement pension at all. However, it may make you better off depending on what you were awarded as it could bring you into entitlement to Pension Credit and (with that) HB and CTR (if applicable)."
Read more at https://community.scope.org.uk/discussion/39606/hi-im-getting-pips-im-enquiring-if-i-get-state-pension-as-well#81Zysxh1AoV4pPS6.99
I hope this helps, and others who know more will be along to advise you.
Warmest best wishes,
Richard