Allow the user to copy and past text in published captivate content

I suggest that you are trying to do something that Captivate was not designed to do - ie using a can opener when a screwdriver will do.

My suggestion would be to take the course and "Print to Handouts" which will give you a word doc, and then either attach it as a downloadable job aid through a url reference in either word or pdf format.  You could also place the pdf in a web object on a slide called "say resource". The end user can copy and paste content at will from either the downloaded job aid in word or pdf format or from the embedded pdf in the web object.

There is a scrolling text area Widget that will facilitate this. Just make sure it's set for Read-Only. Alternatively, if you're capable of some simple HTML markup, you can insert a Web Object on your slide and create your own text box, scroll box, etc. using HTML and CSS (if you want to control the styling).