# duplicateDocument(withContentsOf:copying:displayName:) Creates a new document by reading the contents for the document from another URL, presents its user interface, and returns the document if successful. ``` func duplicateDocument(withContentsOf url: URL, copying duplicateByCopying: Bool, displayName displayNameOrNil: String?) throws -> NSDocument ``` ## Parameters `url` The URL locating the document from which contents of the new document are copied. `duplicateByCopying` If , the contents located at the passed-in URL are copied into a file located in the directory used for the autosaved contents of untitled documents. `displayNameOrNil` If not `nil` then this value is used to derive a display name for the new document that does not match one that is already in use by an open document. ## Return Value The newly created [`NSDocument`](/documentation/AppKit/NSDocument) object, or `nil` if the document could not be created. ## Discussion The default implementation of this method copies the file if specified, determines the type of the document, calls [`makeDocument(for:withContentsOf:ofType:)`](/documentation/AppKit/NSDocumentController/makeDocument(for:withContentsOf:ofType:)) to instantiate it, sends the document `setDisplayName:` to name it if `displayNameOrNil` is not `nil`, calls [`addDocument(_:)`](/documentation/AppKit/NSDocumentController/addDocument(_:)) to record its opening, and sends the document [`makeWindowControllers()`](/documentation/AppKit/NSDocument/makeWindowControllers()) and [`showWindows()`](/documentation/AppKit/NSDocument/showWindows()) messages. The default implementation of this method uses the file coordination mechanism introduced in OS X v10.7. It passes the document to the `NSFileCoordinator` method immediately after calling the [`addDocument(_:)`](/documentation/AppKit/NSDocumentController/addDocument(_:)) method. (The balancing invocation of the method is in the [`NSDocument`](/documentation/AppKit/NSDocument) method [`close()`](/documentation/AppKit/NSDocument/close()).) You can override this method to customize how documents are duplicated. It is called by the [`NSDocument`](/documentation/AppKit/NSDocument) method [`duplicate()`](/documentation/AppKit/NSDocument/duplicate()). It may also be called from other places in AppKit. In most cases, an app does not need to call this method directly. > Handling Errors in Swift: > In Swift, this method returns a nonoptional result and is marked with the `throws` keyword to indicate that it throws an error in cases of failure. > > You call this method in a `try` expression and handle any errors in the `catch` clauses of a `do` statement, as described in [Error Handling](https://docs.swift.org/swift-book/LanguageGuide/ErrorHandling.html) in [The Swift Programming Language](https://docs.swift.org/swift-book/) and `About Imported Cocoa Error Parameters`. --- 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)