Can users copy text from a screen?

I would recommend using the Translation Export function for this - (Click the Articulate icon at the top left>select Translation>Export

This will export all the text to a word document (each text block is automatically given a unique ID).  You can edit the text to fix any typos etc., and then use the Translation>Import function to load the text back into Storyline. It works like a charm as long as you don't edit the IDs themselves.