Fava and beancount have some affordances here. You can make a data directory with a directory structure that matches your chart of accounts. Place datestamped files in here and they'll show up inline in your fava ledger view.

Additionally you can annotate a transaction with a "document" tag and that document will show up directly associated in the ui.

The ui has pretty good previewing for these. I add pdf versions of all of my statements, and attach receipts to specific transactions (business expenses, proof of paying taxes, etc.)

It works quite well