You're on the right track. One key decision to make is whether you want to store the file itself or just a link to the file which is called store by reference.
To get the file to open, try using export field contents from the Edit menu. You can also write a script that uses this command and use a button next to the container field to perform that script step.
Thank you so much! I first tried your suggestion about using "store a reference to the file" and that worked brilliantly!