Open a bill or a journal entry and choose Attach files under Attachments to add JPG, PNG, WebP or PDF files of up to 10 MB each, such as a supplier's bill or a receipt. A journal entry also lists the files on the bill it came from. For a bank transaction, attach the receipt to the journal entry it added.
The files can be opened by anyone who can open the books, including an accountant, and by nobody else.