A good filename answers three questions at a glance: what is the document, when was it created, and which version is this?
Choose a predictable pattern
Use a pattern such as YYYY-MM-DD_document-type_subject_status.pdf and keep the order consistent.
Separate drafts from final files
Avoid labels such as final-final. Use a clear status and a version number while work is active.
Write the rule down
A naming system only works when everyone follows it. Put the pattern in a short team guide and include examples.