CorePDF | A basic PDF library that works with .net core | Document Editor library

import UIKit
import PDFKit

class ViewController: UIViewController {

    @IBOutlet weak var pdfView: PDFView!

    lazy var pdfDoc:PDFDocument? = {
        guard let path = Bundle.main.path(forResource: "6368", ofType: "pdf") else {return nil}
        let url = URL(fileURLWithPath: path)
        return PDFDocument(url: url)
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        self.setupPDFView()
        self.save()
    }

    func setupPDFView() {
        //Setup and put pdf on view
        pdfView.autoScales = true
        pdfView.displayMode = .singlePageContinuous
        pdfView.displayDirection = .horizontal
        pdfView.document = pdfDoc

        self.add(annotation: self.circleAnnotation(), to: 0)
    }

    func add(annotation: PDFAnnotation, to page:Int){
        self.pdfDoc?.page(at: page)?.addAnnotation(annotation)
    }

    func circleAnnotation()->PDFAnnotation {
        let bounds = CGRect(x: 20.0, y: 20.0, width:200.0, height: 200.0)
        let annotation = PDFAnnotation(bounds: bounds, forType: .circle, withProperties: nil)
        annotation.interiorColor = UIColor.black
        return annotation
    }

    func save() {
        //Save to file
        guard let url = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else {return}
        let data = pdfView.document?.dataRepresentation()
        do {
            if data != nil{try data!.write(to: url)}
        } 
        catch {
            print(error.localizedDescription)
        }
    }
}