Is it ok to change "so" to"therefore"?
She wanted to share the secret with her classmates. So, one Friday, Ena went to the front of the classroom, and she told everyone bravely, “I have a wig on.”

Question

Answer

They both mean the same thing IN ESSENCE the same as Because. Even in instances where one is more commonly used, the other could be substituted. As Chris pointed out 'Therefore' is commonly used in mathematical equations. For example,  - 40 celsius = -40 fahrenheit, THEREFORE -40 fahrenheit = -40 celsius. If you switch it to SO it still works - 40 celsius = -40 fahrenheit, SO -40 fahrenheit = -40 celsius.    http://dictionary.reference.com/browse/therefore

Answer

The word " so " is more common. The word " therefore " is used mostly in literature and prepared speeches.

Answer

It works in the sentence but the words are not exactly interchangeable. Using "therefore" here makes it seem like there is a bit more finality than "so."