Export pdf annotations only using preview?

I use Preview on OS X and GoodReader on the iPad for reading and annotating pdfs. GoodReader allows me to 'view summary' which is a plain text list of all highlighted sections and comments added to the pdf. Preview allows you to view annotations in a sidebar but I can't find a way to export them. I really want to create a .txt file of just the pdf's annotations. Does anyone know of a way of doing this, either with Preview or another app whose annotations can be viewed on GoodReader and vice versa?