Question: how to open a photoshop file in camera raw?
Answer: In Photoshop, go to Edit/Photoshop > Preferences (Ctrl-K/Cmd-K) > File Handling.
Under File Compatibility, check Prefer Adobe Camera Raw for Supported Raw Files, then click OK. When you double-click a raw file, it will open into Camera Raw (as opposed to other software that can be used to convert raw files).