You can’t hide all formulas at once because we don’t recommend to do so: this would slow down execution of Excel.
The goal is that if someone manages to remove the protection, protected cells will stop working and thus the workbook becomes useless. So basically, you should choose some cells to protect with XLS Padlock and use the
hidden attribute for all other remaining ones.
There are known tricks to deprotect hidden cells through password cracking, but this requires VBA. If you block access to VBA editor with XLS Padlock, this should be OK.