Run PERSONAL.XLSB macro when any Excel file is opened

Hi all

Hoping this is pretty simple and I'm just being an idiot.
I need to store a macro in PERSONAL.XLSB but I need it to run when any excel file is opened (as it checks what the file contains, then does a lot of work for me.)

I've seen other people have done this, but I can't get it to work for some reason. Any help is appreciated!

Thank you

Aaron