You may need to open the file in Adobe instead. Export Field Contents can export a temporary copy to the user's temporary folder and then open the file with the OS specified default application for that file type. But if the changes made need to be saved back to the container field, you'd need to use a script to insert the newly modified copy back into the original container field.
Thanks Phil. I'm still learning FileMaker Pro and will take your advice. I am about to try writing my first script. :)
And that script needs to do what?
One basic bit of advice that I can share is to try figuring out how to do each step by hand by selecting menu options and clicking items in the tool bar. then write those steps down. Chances are very good that you can find a script step for each step that you wrote down as most FileMaker Script steps directly correspond with a menu option you can select manually.