Reply To: Restyle an ID doc to match another ID doc?

I would create a template from the first doc, and then copy the content from the supplied doc to the template.

And before you do anything make sure all local overrides are properly formatted with character styles. It takes a second. Just fire up Find/Change. In the Find Format field select Italics, and in the Change Format field select your Italics character style. Make sure the scope is the entire document or story and hit Change All. Do the same for bold or any local overrides you want to retain.