By default, SAM is setup to Auto-Rename Documents when uploaded, so when users download them they have a standard descriptive name.
SAM renames documents to "[Entity Name]_[Document Type]". The [Entity Name] is the Full Name of the Main Entity/Record, Family, Person or Organization.
To change this setting:
Settings > Misc Advanced System Settings > Documents | Auto-Rename on Upload
This setting is not applied retroactively. Documents previously uploaded will not be renamed when the setting is changed.
Special Exception: When Documents are uploaded from an Add/Edit form and they are being uploaded at the same time as the Main Entity Record, like a one-part Application Form, the Document will not be Auto-Renamed, because it can't for technical reasons.