Enable PDF Thumbnails
If enabled, in Documents, Workzone automatically creates a thumbnail image of first page of PDF documents; if disabled, Workzone shows the PDF icon.
This settings is found in the GLOBAL SETTINGS section under the settings (gear icon) in the top right for All Workspaces, specifically in the Features to display page, further down in the Other Features section. Only Administrators can set this for your organization.
To enable, check the box on the Enable PDF Thumbnails row. This setting applies to all workspaces and cannot be overridden at the workspace level.