You can attach any document on the Memo tab (as were done when Sage was first used where I work - copies of statements from the old system for some of the customers were so attached), but not to individual transactions which is what I guess you want.  See also:

• Posted 27/04/2023 11:51 Attachment link in the sales invoices similar to the purchase invoices to attached customer purchase order (soft copies)
• Posted 13/04/2023 09:25 Option to attach documents to sales invoices, either in invoice module or in batch invoice screen and on bank payments/receipts
• Posted 23/03/2023 10:16 Add attachments to BP, BR and SI transactions
• Posted 09/03/2023 13:37 Attaching a PDF to a sales invoice
• Posted 18/10/2022 11:01 In Batch invoices for customers the ability to attach a file.
• Posted 06/10/2022 12:24 Be able to add attachments to customers invoices
• Posted 23/09/2022 07:55 Sales Invoice attachments Sage 50 V28.1

There are more on a similar line.

Have you looked at Auto Entry? It has the facility to do Sales Invoices