PDFKit

Display, navigate, search, annotate, and manipulate PDF documents with PDFView, PDFDocument, PDFPage, PDFAnnotation, and PDFSelection.

Workflow

1. Load the document safely, handle password/invalid data, and define who owns mutations and saves.
2. Configure PDFView display, scaling, navigation, and observation for the actual product surface.
3. Perform search, selection, annotation, form, thumbnail, or page operations with PDF coordinate conversion in mind.
4. Keep SwiftUI representable identity stable and strongly own weak delegates/providers.
5. Save to a deliberate destination and verify reload, rotation, large files, protected files, and annotation persistence.

Route by Task

• Read core implementation details for loading, viewing, navigation, search, annotations, thumbnails, SwiftUI integration, and page overlays.
• Read extended PDFKit patterns for forms, watermarks, merging, printing, outlines, custom drawing, and overlay lifecycle recipes.

Core Decisions

• Never assume PDFDocument initialization succeeds or that a protected document is unlocked.
• Convert between view and page coordinates before placing or hit-testing annotations.
• Keep PDF mutations serialized and update UI-facing state on the main actor.
• Avoid representable update loops caused by comparing document objects or rebuilding the view.

Common Mistakes

DON'T: Force-unwrap PDFDocument init

PDFDocument(url:) and PDFDocument(data:) are failable initializers.

// WRONG
let document = PDFDocument(url: url)!

// CORRECT
guard let document = PDFDocument(url: url) else { return }

DON'T: Forget autoScales on PDFView

Without autoScales, the PDF renders at its native resolution.

// WRONG
pdfView.document = document

// CORRECT
pdfView.autoScales = true
pdfView.document = document

DON'T: Ignore PDF coordinate system in annotations

PDF page coordinates have origin at the bottom-left with Y increasing upward -- opposite of UIKit.

// WRONG: UIKit coordinates
let bounds = CGRect(x: 50, y: 50, width: 200, height: 30)

// CORRECT: PDF coordinates (origin bottom-left)
let pageBounds = page.bounds(for: .mediaBox)
let pdfY = pageBounds.height - 50 - 30
let bounds = CGRect(x: 50, y: pdfY, width: 200, height: 30)

DON'T: Modify annotations on a background thread

PDFKit classes are not thread-safe.

// WRONG
DispatchQueue.global().async { page.addAnnotation(annotation) }

// CORRECT
DispatchQueue.main.async { page.addAnnotation(annotation) }

DON'T: Compare PDFDocument with == in UIViewRepresentable

PDFDocument is a reference type. Use identity (!==).

// WRONG: Always replaces document
func updateUIView(_ pdfView: PDFView, context: Context) {
    pdfView.document = document
}

// CORRECT
func updateUIView(_ pdfView: PDFView, context: Context) {
    if pdfView.document !== document {
        pdfView.document = document
    }
}

Review Checklist

• PDFDocument init uses optional binding, not force-unwrap
• pdfView.autoScales = true set for proper initial display
• Page indices checked against pageCount before access
• displayMode and displayDirection configured to match design
• Annotations use PDF coordinate space (origin bottom-left, Y up)
• All PDFKit mutations happen on the main thread
• Password-protected PDFs handled with isLocked / unlock(withPassword:)
• SwiftUI wrapper uses !== identity check in updateUIView
• PDFViewPageChanged notification observed for page tracking
• PDFThumbnailView.pdfView linked to the main PDFView
• Large-document search uses async beginFindString with delegate
• Saved documents use write(to:withOptions:) when encryption needed

References

• Extended patterns (forms, watermarks, merging, printing, overlays, outlines, custom drawing): references/pdfkit-patterns.md
• PDFKit framework
• PDFView
• PDFDocument
• PDFPage, PDFAnnotation, PDFSelection, PDFThumbnailView
• PDFPageOverlayViewProvider
• Adding Widgets to a PDF Document
• Adding Custom Graphics to a PDF
• Core implementation details -- setup, API wiring, and focused implementation recipes moved out of the entrypoint.