Note: This feature has licensing requirements and is available for users and organizations whose administrators have set up sensitivity labels. If you're an administrator looking to get started with sensitivity labels and for more information about the licensing requirements, see Get started with sensitivity labels.
How to configure a default sensitivity label for a SharePoint document library
For an existing document library:
In SharePoint, navigate to the document library > Settings > Library settings.
From the Library settings flyout pane, select Default sensitivity labels, and then select a label from the drop-down box. For example:
Note: If PDF files aren't labeled with this setting, it might be because your admin hasn't enabled PDF support.
If you're creating a new document library, you can configure the same Default sensitivity labels setting from the Create document library flyout pane.