A basic expectation from any document management system is that it should ease the process of document retrieval. Preferably, documents should be uniquely identifiable with a document key or an ID. The Document ID Service in SharePoint helps you to achieve just that. You can activate this service at site collection level by activating the Document ID Service site collection feature.
Go ahead and enable the Document ID Service feature. After enabling the feature, if you upload a new document, you find that a new field called Document ID is now present in the document properties, as shown in Figure 12.1.