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dpearson2699/swift-ios-skills

Agent skills for iOS, iPadOS, Swift, SwiftUI, and modern Apple framework development.

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pdfkit-patterns.mdskills/pdfkit/references/

PDFKit Patterns

Extended patterns for PDFKit: form filling, creating PDFs programmatically, watermarks, printing, merging documents, custom page overlays, document outlines, and custom annotation drawing.

Contents

Form Filling

PDF forms use widget annotations. Each widget has a fieldName, a widgetFieldType, and a widgetStringValue.

Reading Form Fields

func extractFormFields(from document: PDFDocument) -> [(name: String, value: String)] {
    var fields: [(String, String)] = []
    for pageIndex in 0..<document.pageCount {
        guard let page = document.page(at: pageIndex) else { continue }
        for annotation in page.annotations {
            guard annotation.widgetFieldType == .text,
                  let name = annotation.fieldName else { continue }
            fields.append((name, annotation.widgetStringValue ?? ""))
        }
    }
    return fields
}

Filling Text Fields

func fillTextField(in document: PDFDocument, fieldName: String, value: String) {
    for pageIndex in 0..<document.pageCount {
        guard let page = document.page(at: pageIndex) else { continue }
        for annotation in page.annotations {
            if annotation.widgetFieldType == .text,
               annotation.fieldName == fieldName {
                annotation.widgetStringValue = value
                return
            }
        }
    }
}

Filling Checkbox Fields

func setCheckbox(in document: PDFDocument, fieldName: String, checked: Bool) {
    for pageIndex in 0..<document.pageCount {
        guard let page = document.page(at: pageIndex) else { continue }
        for annotation in page.annotations {
            if annotation.widgetFieldType == .button,
               annotation.widgetControlType == .checkBoxControl,
               annotation.fieldName == fieldName {
                annotation.buttonWidgetState = checked ? .onState : .offState
                return
            }
        }
    }
}

Creating Widget Annotations

// Text field widget
func createTextField(
    bounds: CGRect,
    fieldName: String,
    placeholder: String = ""
) -> PDFAnnotation {
    let widget = PDFAnnotation(bounds: bounds, forType: .widget, withProperties: nil)
    widget.widgetFieldType = .text
    widget.fieldName = fieldName
    widget.widgetStringValue = placeholder
    widget.font = UIFont.systemFont(ofSize: 12)
    widget.backgroundColor = UIColor.systemGray6
    return widget
}

// Checkbox widget
func createCheckbox(bounds: CGRect, fieldName: String) -> PDFAnnotation {
    let widget = PDFAnnotation(bounds: bounds, forType: .widget, withProperties: nil)
    widget.widgetFieldType = .button
    widget.widgetControlType = .checkBoxControl
    widget.fieldName = fieldName
    widget.buttonWidgetState = .offState
    return widget
}

// Radio button widget
func createRadioButton(
    bounds: CGRect,
    groupName: String,
    stateString: String
) -> PDFAnnotation {
    let widget = PDFAnnotation(bounds: bounds, forType: .widget, withProperties: nil)
    widget.widgetFieldType = .button
    widget.widgetControlType = .radioButtonControl
    widget.fieldName = groupName
    widget.buttonWidgetStateString = stateString
    return widget
}

// Choice widget (dropdown)
func createDropdown(
    bounds: CGRect,
    fieldName: String,
    options: [String]
) -> PDFAnnotation {
    let widget = PDFAnnotation(bounds: bounds, forType: .widget, withProperties: nil)
    widget.widgetFieldType = .choice
    widget.fieldName = fieldName
    widget.choices = options
    widget.isListChoice = false  // false = dropdown, true = list box
    return widget
}

Building a Simple Form

func buildForm() -> PDFDocument {
    let document = PDFDocument()
    let page = PDFPage()
    let pageBounds = CGRect(x: 0, y: 0, width: 612, height: 792) // Letter size
    page.setBounds(pageBounds, for: .mediaBox)

    // Name field
    let nameField = createTextField(
        bounds: CGRect(x: 100, y: 700, width: 200, height: 24),
        fieldName: "name",
        placeholder: ""
    )
    page.addAnnotation(nameField)

    // Agree checkbox
    let checkbox = createCheckbox(
        bounds: CGRect(x: 100, y: 660, width: 20, height: 20),
        fieldName: "agree"
    )
    page.addAnnotation(checkbox)

    document.insert(page, at: 0)
    return document
}

Creating PDFs Programmatically

From Images

func createPDFFromImages(_ images: [UIImage]) -> PDFDocument {
    let document = PDFDocument()
    for (index, image) in images.enumerated() {
        if let page = PDFPage(image: image) {
            document.insert(page, at: index)
        }
    }
    return document
}

From Images with Options

func createPDFFromImage(
    _ image: UIImage,
    mediaBox: CGRect? = nil,
    compressionQuality: CGFloat = 0.8
) -> PDFPage? {
    var options: [PDFPage.ImageInitializationOption: Any] = [
        .compressionQuality: compressionQuality
    ]
    if let box = mediaBox {
        options[.mediaBox] = NSValue(cgRect: box)
    }
    return PDFPage(image: image, options: options)
}

Using Core Graphics

For full control over PDF layout, use UIGraphicsPDFRenderer.

func createPDFWithCoreGraphics() -> Data {
    let pageRect = CGRect(x: 0, y: 0, width: 612, height: 792)
    let renderer = UIGraphicsPDFRenderer(bounds: pageRect)

    return renderer.pdfData { context in
        context.beginPage()

        // Draw title
        let title = "Document Title"
        let titleAttributes: [NSAttributedString.Key: Any] = [
            .font: UIFont.boldSystemFont(ofSize: 24),
            .foregroundColor: UIColor.black
        ]
        title.draw(at: CGPoint(x: 50, y: 50), withAttributes: titleAttributes)

        // Draw body text
        let body = "This is the body text of the PDF document."
        let bodyAttributes: [NSAttributedString.Key: Any] = [
            .font: UIFont.systemFont(ofSize: 12),
            .foregroundColor: UIColor.darkGray
        ]
        let bodyRect = CGRect(x: 50, y: 100, width: 512, height: 600)
        body.draw(in: bodyRect, withAttributes: bodyAttributes)

        // Draw a line
        context.cgContext.setStrokeColor(UIColor.gray.cgColor)
        context.cgContext.setLineWidth(1)
        context.cgContext.move(to: CGPoint(x: 50, y: 90))
        context.cgContext.addLine(to: CGPoint(x: 562, y: 90))
        context.cgContext.strokePath()
    }
}

Loading Core Graphics PDF into PDFDocument

let pdfData = createPDFWithCoreGraphics()
let document = PDFDocument(data: pdfData)

Watermarks

Add watermarks by subclassing PDFPage and overriding draw(with:to:).

Text Watermark

class WatermarkedPage: PDFPage {
    var watermarkText: String = "CONFIDENTIAL"

    override func draw(with box: PDFDisplayBox, to context: CGContext) {
        super.draw(with: box, to: context)

        UIGraphicsPushContext(context)
        context.saveGState()

        let pageBounds = bounds(for: box)
        let center = CGPoint(x: pageBounds.midX, y: pageBounds.midY)

        // Rotate around center
        context.translateBy(x: center.x, y: center.y)
        context.rotate(by: -.pi / 4)  // -45 degrees
        context.translateBy(x: -center.x, y: -center.y)

        let attributes: [NSAttributedString.Key: Any] = [
            .font: UIFont.boldSystemFont(ofSize: 72),
            .foregroundColor: UIColor.red.withAlphaComponent(0.15)
        ]

        let textSize = watermarkText.size(withAttributes: attributes)
        let textOrigin = CGPoint(
            x: center.x - textSize.width / 2,
            y: center.y - textSize.height / 2
        )
        watermarkText.draw(at: textOrigin, withAttributes: attributes)

        context.restoreGState()
        UIGraphicsPopContext()
    }
}

Applying Watermarks via Document Delegate

class WatermarkDelegate: NSObject, PDFDocumentDelegate {
    func classForPage() -> AnyClass {
        WatermarkedPage.self
    }
}

// Usage
let delegate = WatermarkDelegate()
document.delegate = delegate
pdfView.document = document

Image Watermark

class ImageWatermarkedPage: PDFPage {
    var watermarkImage: UIImage?

    override func draw(with box: PDFDisplayBox, to context: CGContext) {
        super.draw(with: box, to: context)

        guard let image = watermarkImage?.cgImage else { return }

        let pageBounds = bounds(for: box)
        let imageSize = CGSize(width: 200, height: 200)
        let imageRect = CGRect(
            x: pageBounds.midX - imageSize.width / 2,
            y: pageBounds.midY - imageSize.height / 2,
            width: imageSize.width,
            height: imageSize.height
        )

        context.saveGState()
        context.setAlpha(0.1)
        context.draw(image, in: imageRect)
        context.restoreGState()
    }
}

Merging Documents

Append All Pages

func mergeDocuments(_ documents: [PDFDocument]) -> PDFDocument {
    let merged = PDFDocument()
    var insertIndex = 0
    for document in documents {
        for pageIndex in 0..<document.pageCount {
            guard let page = document.page(at: pageIndex) else { continue }
            merged.insert(page, at: insertIndex)
            insertIndex += 1
        }
    }
    return merged
}

Extract Page Range

func extractPages(
    from document: PDFDocument,
    range: ClosedRange<Int>
) -> PDFDocument {
    let extracted = PDFDocument()
    var insertIndex = 0
    for pageIndex in range {
        guard pageIndex >= 0,
              pageIndex < document.pageCount,
              let page = document.page(at: pageIndex) else { continue }
        extracted.insert(page, at: insertIndex)
        insertIndex += 1
    }
    return extracted
}

Split Document

func splitDocument(_ document: PDFDocument, pagesPerChunk: Int) -> [PDFDocument] {
    var chunks: [PDFDocument] = []
    var chunkDoc = PDFDocument()
    var chunkIndex = 0

    for pageIndex in 0..<document.pageCount {
        guard let page = document.page(at: pageIndex) else { continue }
        chunkDoc.insert(page, at: chunkIndex)
        chunkIndex += 1

        if chunkIndex >= pagesPerChunk {
            chunks.append(chunkDoc)
            chunkDoc = PDFDocument()
            chunkIndex = 0
        }
    }

    if chunkDoc.pageCount > 0 {
        chunks.append(chunkDoc)
    }

    return chunks
}

Printing

Using UIPrintInteractionController

func printPDF(document: PDFDocument, from viewController: UIViewController) {
    guard let data = document.dataRepresentation() else { return }

    let printController = UIPrintInteractionController.shared
    let printInfo = UIPrintInfo(dictionary: nil)
    printInfo.outputType = .general
    printInfo.jobName = "PDF Document"

    printController.printInfo = printInfo
    printController.printingItem = data
    printController.present(animated: true)
}

Print a Specific Page Range

func printPageRange(
    document: PDFDocument,
    range: ClosedRange<Int>,
    from viewController: UIViewController
) {
    let subset = extractPages(from: document, range: range)
    guard let data = subset.dataRepresentation() else { return }

    let printController = UIPrintInteractionController.shared
    let printInfo = UIPrintInfo(dictionary: nil)
    printInfo.outputType = .general
    printController.printInfo = printInfo
    printController.printingItem = data
    printController.present(animated: true)
}

Document Outlines

PDFOutline represents the table of contents (bookmarks) of a PDF.

Reading Outlines

func printOutline(_ outline: PDFOutline, level: Int = 0) {
    let indent = String(repeating: "  ", count: level)
    if let label = outline.label {
        print("\(indent)\(label)")
    }
    for i in 0..<outline.numberOfChildren {
        if let child = outline.child(at: i) {
            printOutline(child, level: level + 1)
        }
    }
}

// Usage
if let root = document.outlineRoot {
    printOutline(root)
}

Creating Outlines

func buildOutline(for document: PDFDocument) {
    let root = PDFOutline()

    func destination(for pageIndex: Int) -> PDFDestination? {
        guard pageIndex >= 0,
              pageIndex < document.pageCount,
              let page = document.page(at: pageIndex) else { return nil }
        return PDFDestination(page: page, at: .zero)
    }

    let chapter1 = PDFOutline()
    chapter1.label = "Chapter 1"
    chapter1.destination = destination(for: 0)
    root.insertChild(chapter1, at: 0)

    let section1_1 = PDFOutline()
    section1_1.label = "Section 1.1"
    section1_1.destination = destination(for: 2)
    chapter1.insertChild(section1_1, at: 0)

    let chapter2 = PDFOutline()
    chapter2.label = "Chapter 2"
    chapter2.destination = destination(for: 5)
    root.insertChild(chapter2, at: 1)

    document.outlineRoot = root
}

Navigating to an Outline Entry

func goToOutlineEntry(_ outline: PDFOutline, in pdfView: PDFView) {
    if let destination = outline.destination {
        pdfView.go(to: destination)
    } else if let action = outline.action {
        pdfView.perform(action)
    }
}

Custom Annotation Subclasses

Override draw(with:in:) to render custom annotation graphics.

class CircleStampAnnotation: PDFAnnotation {
    override func draw(with box: PDFDisplayBox, in context: CGContext) {
        super.draw(with: box, in: context)

        UIGraphicsPushContext(context)
        context.saveGState()

        let insetBounds = bounds.insetBy(dx: 2, dy: 2)
        let path = UIBezierPath(ovalIn: insetBounds)
        path.lineWidth = 3

        UIColor.systemRed.setStroke()
        path.stroke()

        // Draw centered text
        let text = "REVIEWED"
        let attributes: [NSAttributedString.Key: Any] = [
            .font: UIFont.boldSystemFont(ofSize: 10),
            .foregroundColor: UIColor.systemRed
        ]
        let textSize = text.size(withAttributes: attributes)
        let textOrigin = CGPoint(
            x: bounds.midX - textSize.width / 2,
            y: bounds.midY - textSize.height / 2
        )
        text.draw(at: textOrigin, withAttributes: attributes)

        context.restoreGState()
        UIGraphicsPopContext()
    }
}

Registering Custom Annotations via Delegate

class AnnotationDelegate: NSObject, PDFDocumentDelegate {
    func `class`(forAnnotationType annotationType: String) -> AnyClass {
        switch annotationType {
        case "CircleStamp":
            return CircleStampAnnotation.self
        default:
            return PDFAnnotation.self
        }
    }
}

Custom Page Subclasses

Override draw(with:to:) for page-level custom drawing like headers, footers, or decorative borders.

class HeaderFooterPage: PDFPage {
    var headerText: String = ""
    var footerText: String = ""

    override func draw(with box: PDFDisplayBox, to context: CGContext) {
        super.draw(with: box, to: context)

        UIGraphicsPushContext(context)
        context.saveGState()

        let pageBounds = bounds(for: box)
        let attributes: [NSAttributedString.Key: Any] = [
            .font: UIFont.systemFont(ofSize: 10),
            .foregroundColor: UIColor.gray
        ]

        // Header (top of page in PDF coordinates)
        if !headerText.isEmpty {
            let headerSize = headerText.size(withAttributes: attributes)
            let headerOrigin = CGPoint(
                x: pageBounds.midX - headerSize.width / 2,
                y: pageBounds.maxY - 30
            )
            headerText.draw(at: headerOrigin, withAttributes: attributes)
        }

        // Footer (bottom of page in PDF coordinates)
        if !footerText.isEmpty {
            let footerSize = footerText.size(withAttributes: attributes)
            let footerOrigin = CGPoint(
                x: pageBounds.midX - footerSize.width / 2,
                y: 20
            )
            footerText.draw(at: footerOrigin, withAttributes: attributes)
        }

        context.restoreGState()
        UIGraphicsPopContext()
    }
}

Page Overlay Lifecycle

PDFView.pageOverlayViewProvider is weak. Store the provider on a view controller, SwiftUI coordinator, or another object that outlives the PDFView.

PDFKit requests overlay views for pages it is preparing or displaying, then calls the lifecycle hooks as pages enter and leave the visible range. Keep overlay state outside the view so scrolling does not discard edits.

class PageOverlayProvider: NSObject, PDFPageOverlayViewProvider {
    private var pageNotes: [PDFPage: String] = [:]

    func pdfView(_ view: PDFView, overlayViewFor page: PDFPage) -> UIView? {
        let textView = UITextView()
        textView.text = pageNotes[page] ?? ""
        textView.backgroundColor = .clear
        return textView
    }

    func pdfView(
        _ view: PDFView,
        willEndDisplayingOverlayView overlayView: UIView,
        for page: PDFPage
    ) {
        if let textView = overlayView as? UITextView {
            pageNotes[page] = textView.text
        }
    }
}

Overlay views are UIKit/AppKit views, not PDF content. Before calling write(to:) or dataRepresentation(), convert overlay data into PDF annotations, custom annotation appearance streams, or rendered page content. Use .burnInAnnotationsOption when saved annotations should become permanent page content.

Rendering Pages to Images

Single Page

func renderPage(_ page: PDFPage, scale: CGFloat = 2.0) -> UIImage? {
    let pageBounds = page.bounds(for: .mediaBox)
    let size = CGSize(
        width: pageBounds.width * scale,
        height: pageBounds.height * scale
    )

    let renderer = UIGraphicsImageRenderer(size: size)
    return renderer.image { ctx in
        ctx.cgContext.scaleBy(x: scale, y: scale)

        // White background
        UIColor.white.setFill()
        ctx.fill(CGRect(origin: .zero, size: size))

        // PDFPage draw uses bottom-left origin; flip the context
        ctx.cgContext.translateBy(x: 0, y: pageBounds.height)
        ctx.cgContext.scaleBy(x: 1, y: -1)

        page.draw(with: .mediaBox, to: ctx.cgContext)
    }
}

Thumbnail Shortcut

The simpler thumbnail(of:for:) method handles coordinate flipping internally.

let thumbnail = page.thumbnail(of: CGSize(width: 200, height: 260), for: .mediaBox)

Page Rotation and Cropping

Rotation

// Rotate a page (must be a multiple of 90)
page.rotation = 90   // 0, 90, 180, or 270

Cropping

Set the crop box to display only a portion of the page.

let pageBounds = page.bounds(for: .mediaBox)
let cropRect = pageBounds.insetBy(dx: 50, dy: 50)
page.setBounds(cropRect, for: .cropBox)

Burning In Annotations

Write annotations permanently into the PDF content so they cannot be removed.

func burnInAnnotations(_ document: PDFDocument, to url: URL) -> Bool {
    document.write(to: url, withOptions: [
        .burnInAnnotationsOption: true
    ])
}

After burning in, annotations become part of the page content and are no longer editable or removable as separate objects.

Document Permissions

Check what operations the PDF allows.

func checkPermissions(_ document: PDFDocument) {
    let status = document.permissionsStatus  // .none, .user, .owner

    let canCopy = document.allowsCopying
    let canPrint = document.allowsPrinting
    let canComment = document.allowsCommenting
    let canFillForms = document.allowsFormFieldEntry
    let canAssemble = document.allowsDocumentAssembly
    let canModify = document.allowsDocumentChanges
    let canAccessibility = document.allowsContentAccessibility
}

Writing with Access Permissions

func saveWithRestrictions(_ document: PDFDocument, to url: URL) {
    let permissions: PDFAccessPermissions = [
        .allowsLowQualityPrinting,
        .allowsContentCopying,
        .allowsCommenting
    ]
    document.write(to: url, withOptions: [
        .ownerPasswordOption: "ownerSecret",
        .userPasswordOption: "userPass",
        .accessPermissionsOption: permissions.rawValue
    ])
}

Coordinator Pattern for PDFView

A reusable coordinator that handles delegate callbacks, notifications, and annotation hit detection for a SwiftUI-wrapped PDFView.

import SwiftUI
import PDFKit

struct ManagedPDFView: UIViewRepresentable {
    let document: PDFDocument
    @Binding var currentPageIndex: Int
    var onAnnotationTapped: ((PDFAnnotation) -> Void)?

    func makeUIView(context: Context) -> PDFView {
        let pdfView = PDFView()
        pdfView.autoScales = true
        pdfView.displayMode = .singlePageContinuous
        pdfView.document = document
        pdfView.delegate = context.coordinator
        context.coordinator.attach(to: pdfView)
        return pdfView
    }

    func updateUIView(_ pdfView: PDFView, context: Context) {
        if pdfView.document !== document {
            pdfView.document = document
        }
        if currentPageIndex >= 0,
           currentPageIndex < document.pageCount,
           let page = document.page(at: currentPageIndex),
           pdfView.currentPage !== page {
            pdfView.go(to: page)
        }
    }

    static func dismantleUIView(_ uiView: PDFView, coordinator: Coordinator) {
        NotificationCenter.default.removeObserver(coordinator)
    }

    func makeCoordinator() -> Coordinator { Coordinator(self) }

    class Coordinator: NSObject, PDFViewDelegate {
        let parent: ManagedPDFView

        init(_ parent: ManagedPDFView) {
            self.parent = parent
            super.init()
        }

        func attach(to pdfView: PDFView) {
            NotificationCenter.default.removeObserver(self)
            NotificationCenter.default.addObserver(
                self,
                selector: #selector(pageChanged),
                name: .PDFViewPageChanged,
                object: pdfView
            )
            NotificationCenter.default.addObserver(
                self,
                selector: #selector(annotationHit),
                name: .PDFViewAnnotationHit,
                object: pdfView
            )
        }

        deinit {
            NotificationCenter.default.removeObserver(self)
        }

        @objc func pageChanged(_ notification: Notification) {
            guard let pdfView = notification.object as? PDFView,
                  let page = pdfView.currentPage,
                  let doc = pdfView.document else { return }
            let index = doc.index(for: page)
            if parent.currentPageIndex != index {
                parent.currentPageIndex = index
            }
        }

        @objc func annotationHit(_ notification: Notification) {
            guard let annotation = notification.userInfo?["PDFAnnotationHit"] as? PDFAnnotation
            else { return }
            parent.onAnnotationTapped?(annotation)
        }

        func pdfViewWillClick(onLink sender: PDFView, with url: URL) {
            UIApplication.shared.open(url)
        }
    }
}

skills

pdfkit

references

pdfkit-patterns.md

SKILL.md

README.md

tile.json