Encrypt XFDF PDFs on-the-fly Using Swift for iOS

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//
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//  Copyright © 2021-2025 PSPDFKit GmbH. All rights reserved.
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//
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//  The Nutrient sample applications are licensed with a modified BSD license.
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//  Please see License for details. This notice may not be removed from this file.
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//
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import PSPDFKit
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import PSPDFKitUI
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class EncryptedXFDFAnnotationProviderExample: Example {
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    override init() {
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        super.init()
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        title = "XFDF Annotation Provider, Encrypted"
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        contentDescription = "Variant that encrypts/decrypts the XFDF file on-the-fly."
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        category = .annotationProviders
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        priority = 81
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    }
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    // This example shows how you can create an XFDF provider instead of the default file-based one.
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    // XFDF is an industry standard and the file will be interopable with Adobe Acrobat or any other standard-compliant PDF framework.
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    override func invoke(with delegate: ExampleRunnerDelegate?) -> UIViewController? {
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        let documentURL = AssetLoader.assetURL(for: .annualReport)
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        // Load from an example XFDF file.
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        let passphraseProvider = { () -> String in
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            return "jJ9A3BiMXoq+rEoYMdqBoBNzgxagTf"
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        }
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        let docsFolder = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
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        let fileXML = docsFolder.appendingPathComponent("XFDFTest-encrypted.xfdf")
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        print("Using XFDF file at \(fileXML.path)")
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        // DEBUG HELPER: delete existing file.
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        // try? FileManager.default.removeItem(at: fileXML)
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        // Create an example XFDF from the current document if one doesn't already exist.
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        if !FileManager.default.fileExists(atPath: fileXML.path) {
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            // Collect all existing annotations from the document
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            let tempDocument = Document(url: documentURL)
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            let annotations = tempDocument.allAnnotations(of: .all).values.flatMap { $0 }
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            // Write the annotations to the disk creating a new XFDF file.
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            let dataSink = AESCryptoDataSink(url: fileXML, passphraseProvider: passphraseProvider)
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            do {
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                try XFDFWriter().write(annotations, to: dataSink, documentProvider: tempDocument.documentProviders.first!)
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            } catch {
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                print("Failed to write XFDF file: \(error.localizedDescription)")
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            }
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        }
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        guard let cryptoDataProvider = AESCryptoDataProvider(url: fileXML, passphraseProvider: passphraseProvider) else {
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            print("Error creating crypto data provider")
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            return nil
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        }
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        // Create document and set up the XFDF provider.
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        let document = Document(url: documentURL)
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        document.annotationSaveMode = .externalFile
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        document.didCreateDocumentProviderBlock = { documentProvider in
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            let XFDFProvider = XFDFAnnotationProvider(documentProvider: documentProvider, dataProvider: cryptoDataProvider)
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            // Note that if the document you're opening has form fields which you wish to be usable when using XFDF, you should also add the file annotation
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            // provider to the annotation manager's `annotationProviders` array:
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            //
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            // let fileProvider = documentProvider.annotationManager.fileAnnotationProvider!
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            // documentProvider.annotationManager.annotationProviders = [XFDFProvider, fileProvider]
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            documentProvider.annotationManager.annotationProviders = [XFDFProvider]
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        }
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        return PDFViewController(document: document)
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    }
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}