So in Tkinter, you can only do one function at a time so if there is a function/process going on then the whole Tkinter GUI will freeze until it completes. Whenever the text or pdf text-to-speech conversion is going you can't do anything else, not even close it until you brute force kill it via task manager or interrupt the ongoing Thread.

In the pdf menu when you start the conversion another Thread is started for that, so you can still use the GUI while listening to the pdf file. But if you close the GUI while the speaker is still in the middle of the conversion, GUI will close and you will be left with a Zombie Thread still speaking the pdf content.

It’ll help with the dependencies. https://docs.python.org/3/library/venv.html