Can you expand a bit about the nature of the business? Is all of this paperwork constantly trickling in or does it show up at different times of the day or by the activity that created the paperwork? Any kind of way to sort it out or prioritize? Can your boss help to make a flow chart?
Once upon a time I had to learn how to do a promotion job with almost no training and no ONE person to go to. I learned by trial-and-error, looking through old files, and outdated training materials. But I excelled in a few short months of the routine.
They wouldn’t have promoted you if you didn’t have potential! Try to break down what help you need into categories (if you can) or tell your boss that there is something you’re just not “getting” and would like some more direction getting to that AHA! Or if there’s “just too much”, ways to streamline/steps to skip until there’s a lull?