Typing over text? pls help!

Hi, i don't know if this is just because im relatively new to storyline of if im just an idiot, but if i copy text from a word document over to a storyline text box and i want to edit the text or add tabs or do any modifications, it seems to be typing over the text that's in there, so then every time i have to go and fix it in word first and then again copy it over.... cant find any Options that could switch it off? 

Any help with this issue would be Greatly Apprecited!!!!

Thank you