Start with the evidence
Choose a simple order for date, merchant and reference, and use it consistently. Avoid putting sensitive account information into a filename that may appear in shared lists or notifications.
Work through the example
2026-10-08-example-cafe-R718 identifies more than scan-final-new.pdf. The name still needs checking against the source; a well-formatted label can contain a copied date or reference.
Make the next step clear
Document the convention and keep exceptions understandable. If a source is renamed, preserve its content and links. Do not depend on a filename alone to decide whether two documents are duplicates.
Keep the source context
A readable source and a clear label serve different purposes. Keep the original document intact while adding searchable context around it. Avoid treating filenames, OCR output or a cropped image as more authoritative than the actual source.