# HKDocumentSample An abstract class that represents a health document in the HealthKit store. ``` class HKDocumentSample ``` ## Overview You should never instantiate an `HKDocumentSample` object directly. Instead, you always work with a concrete subclass. In iOS 10 and watchOS 3, the only concrete class is the [`HKCDADocumentSample`](/documentation/HealthKit/HKCDADocumentSample) class. Document samples are immutable: You set the sample’s properties when you create it, and they cannot change. ### Extend Document Samples Like many HealthKit classes, you should not create any custom subclasses of the `HKDocumentSample` class. You can extend the `HKDocumentSample` class and its subclasses by adding custom metadata keys and values to the metadata dictionary when the object is instantiated. ## Topics ### Accessing the Document Sample Properties [`documentType`](/documentation/HealthKit/HKDocumentSample/documentType) The type of document represented by the sample. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)