Nothing really to get your head around. Open the process workbook. Click the button on the Add-Ins tab and follow the instructions. Test with the workbooks you provided.

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Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com

Sorry - when I posted my initial reply I hadn't, at that stage, discovered how your process actually worked!!

I have now tested it and am very impressed. If it wouldn't take much more of your time could I ask two follow-up questions?
1. Would it be easy to adapt the coding to simply put the information from the Bank Transactions file into the Ledger (without attempting to fill the 5 Project cells) if the donor's information wasn't already in the Donors file? I got an error when it came to a new credit which hadn't been identified in the Donors file in advance. I would prefer in such a situation to populate the first 3 columns in the Ledger only (rather than stop the process with an error message).
2. If at some future date we were to change the layout of the Ledger (with additional columns inserted) where would I go looking for the piece of coding that I could adapt to find the right columns?

I really appreciate the work that you have put into this - it will certainly improve the ease with which the charity can handle their monthly recording of credits.