To attach files usually requires that the be compacted then zipped. Forum limit is 2 Mb, I think.
Sounds like you are creating calculated table fields - not advisable. Then again, you mention forms, so can't tell where the calculation is performed. Or is it concatenation?
As for subform relationship, do you have any parent/child fields set? Sometimes the appending of subform records is done as they are created, sometimes when clicking a button, sometimes when closing the main form. Depends on the situation and what you need to do, but in most cases you want to prevent the possibility of anyone attempting to create subform records when there's no primary record yet.
Welcome to the forum, btw.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.