# ReferenceFileDocument A type that you use to serialize reference type documents to and from file. ``` @preconcurrency protocol ReferenceFileDocument : ObservableObject, Sendable ``` ## Overview To store a document as a reference type — like a class — create a type that conforms to the `ReferenceFileDocument` protocol and implement the required methods and properties. Your implementation: - Provides a list of the content types that the document can read from and write to by defining [`readableContentTypes`](/documentation/SwiftUI/ReferenceFileDocument/readableContentTypes). If the list of content types that the document can write to is different from those that it reads from, you can optionally also define [`writableContentTypes`](/documentation/SwiftUI/ReferenceFileDocument/writableContentTypes). - Loads documents from file in the [`init(configuration:)`](/documentation/SwiftUI/ReferenceFileDocument/init(configuration:)) initializer. - Stores documents to file by providing a snapshot of the document’s content in the [`snapshot(contentType:)`](/documentation/SwiftUI/ReferenceFileDocument/snapshot(contentType:)) method, and then serializing that content in the [`fileWrapper(snapshot:configuration:)`](/documentation/SwiftUI/ReferenceFileDocument/fileWrapper(snapshot:configuration:)) method. Ensure that types that conform to this protocol are `Sendable`. In particular, SwiftUI calls the protocol’s methods from different isolation domains. Don’t perform serialization and deserialization on `MainActor`. ``` final class PDFDocument: ReferenceFileDocument { struct Storage { var contents: Data } static let readableContentTypes: [UTType] = [.pdf] let storage: Mutex required init(configuration: ReadConfiguration) throws { guard let data = configuration.file.regularFileContents else { throw CocoaError(.fileReadCorruptFile) } self.storage = .init(.init(contents: data)) } func snapshot(contentType: UTType) throws -> Data { storage.withLock { $0.contents } } func fileWrapper(snapshot: Data, configuration: WriteConfiguration) throws -> FileWrapper { return FileWrapper(regularFileWithContents: snapshot) } } ``` > Important: If you store your document as a value type — like a > structure — use ``doc://com.apple.SwiftUI/documentation/SwiftUI/FileDocument`` instead. ## Topics ### Reading a document [`init(configuration:)`](/documentation/SwiftUI/ReferenceFileDocument/init(configuration:)) Creates a document and initializes it with the contents of a file. [`readableContentTypes`](/documentation/SwiftUI/ReferenceFileDocument/readableContentTypes) The file and data types that the document reads from. [`ReferenceFileDocument.ReadConfiguration`](/documentation/SwiftUI/ReferenceFileDocument/ReadConfiguration) The configuration for reading document contents. ### Getting a snapshot [`snapshot(contentType:)`](/documentation/SwiftUI/ReferenceFileDocument/snapshot(contentType:)) Creates a snapshot that represents the current state of the document. [`Snapshot`](/documentation/SwiftUI/ReferenceFileDocument/Snapshot) A type that represents the document’s stored content. ### Writing a document [`fileWrapper(snapshot:configuration:)`](/documentation/SwiftUI/ReferenceFileDocument/fileWrapper(snapshot:configuration:)) Serializes a document snapshot to a file wrapper. [`writableContentTypes`](/documentation/SwiftUI/ReferenceFileDocument/writableContentTypes) The file types that the document supports saving or exporting to. [`ReferenceFileDocument.WriteConfiguration`](/documentation/SwiftUI/ReferenceFileDocument/WriteConfiguration) The configuration for writing document contents. --- 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)