Switches for PCB: Mounting and hole questions
For this part to properly be mounted to the PCB, it needs to have holes slightly bigger than the pin sizes.  In the datasheet, there is always a section that shows the required hole sizes as well as the measurements for each pin.  

The two squares holes do not necessary need to be squared.  They can be round holes.  Round holes are the most common type of holes on a PCB for through holes components.  Just make sure the diameter of the round hole exceeds the diagonal length of the square and you should be fine.  You will require a bit more solder to fully mount the switch but it's nothing to be worried about.