adding a Convert.ToInt32 Method

I have my code that's part of a BDC Model I'm creating...

{
            ABCDataContext context = GetDBContext();
            var item = (from e in context.TPFStatus.AsEnumerable()

                        where e.Document_Number == id

                        select e).Single();
            return item;

       }

This would be fine if "Document_Number" was a int as well but its a string. I need to convert from a string to an int. How would I go about adding this to my script...

public static int ToInt32(
        long value
)

I can't get anything I try to work.