Sometimes a mouse is more than just a mouse. For instance, some computer mice can use their extra buttons as shortcuts for common actions: Cut, Copy, & Paste.
If you use mouse-button shortcuts to cut, copy, or paste items on your computer, there is a chance that those buttons will not work inside the PERRLA Add-in for Word. This is because Microsoft Word uses a streamlined internet browser (Internet Explorer 11, Edge, etc.) for Add-ins.
PERRLA hasn't disabled your button clicks – Word has.
Luckily, you can still use the built-in cut, copy, and paste functions in Word & their corresponding keyboard shortcuts.