Ruby gem从可填写的PDF中提取表单数据

We are encountering PDF files that are fillable PDF forms containing user-supplied data. We'd like to extract the data the the user filled into the form but don't know of any gems that exist with this capability. So, for example, there's a field in the PDF form for "First name" which the user has completed with "David" -- we want to get our hands on the data such as "First name=>David"We are encountering PDF files that are fillable