Thanks for taking the time to answer.
The file I'm thinking of at the moment is actually a payment summary, so it's not the same as the receipt created by the debit machine. I would like to share it with the individual students somewhere they can access repeatedly. In the past we have emailed these documents out but when students need them in the future they often can't find the original email and contact us again and it's a big hassle.
How would you suggest we set up the Assignment module to do this? Can we create an assignment that's completely unlinked from the gradebook? And can we post a feedback document without the student having to take any action first?
You asked two questions here:
"Can we create an assignment that's completely unlinked from the gradebook?"
Any Assignment can be excluded from the Gradebook, so it Don's have to affect your course Grades
See this page as your starting point: https://docs.moodle.org/36/en/Grades_FAQ
Look for "How can I grade some of my activities without the results affecting my students' course total?" section.
"...can we post a feedback document without the student having to take any action first?"
Good question, and I'm not sure, because I've never tried that!
Usually a learner would submit something, and a teacher would attach a feedback file.
So I think you should just setup an Assignment and test who you want to do, to see if it can be done?