Converting PDF to Image - Swift iOS

I am trying to convert a PDF file and all its pages to png images.

I have put together the code below filling the example on this thread How to convert PDF to PNG efficiently?

When I run the code, it crashes on the pdf file source (sourceURL) there is definitely a file there. and when I print sourceURl it prints the URL to the file.

The crash says it found nil - My understanding is that means it could not find the file? even though I can physically see and open the file and also print the URL to the file.

Can someone point out what I'm doing wrong?

Code:

func convertPDFtoPNG() {
    let sourceURL = pptURL
    print("pptURL:", pptURL!)
    let destinationURL = pngURL
    let urls = try? convertPDF(at: sourceURL!, to: destinationURL!, fileType: .png, dpi: 200)
}
func convertPDF(at sourceURL: URL, to destinationURL: URL, fileType: ImageFileType, dpi: CGFloat = 200) throws -> [URL] {
    let pdfDocument: CGPDFDocument! = CGPDFDocument(sourceURL as CFURL)!  //Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

    let colorSpace = CGColorSpaceCreateDeviceRGB()
    let bitmapInfo = CGImageAlphaInfo.noneSkipLast.rawValue

    var urls = [URL](repeating: URL(fileURLWithPath : "/"), count: pdfDocument.numberOfPages)
    DispatchQueue.concurrentPerform(iterations: pdfDocument.numberOfPages) { i in

        let pdfPage = pdfDocument.page(at: i + 1)!

        let mediaBoxRect = pdfPage.getBoxRect(.mediaBox)
        let scale = dpi / 72.0
        let width = Int(mediaBoxRect.width * scale)
        let height = Int(mediaBoxRect.height * scale)

        let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: bitmapInfo)!
        context.interpolationQuality = .high
        context.fill(CGRect(x: 0, y: 0, width: width, height: height))
        context.scaleBy(x: scale, y: scale)
        context.drawPDFPage(pdfPage)

        let image = context.makeImage()!
        let imageName = sourceURL.deletingPathExtension().lastPathComponent
        let imageURL = destinationURL.appendingPathComponent("\(imageName)-Page\(i+1).\(fileType.fileExtention)")

        let imageDestination = CGImageDestinationCreateWithURL(imageURL as CFURL, fileType.uti, 1, nil)!
        CGImageDestinationAddImage(imageDestination, image, nil)
        CGImageDestinationFinalize(imageDestination)

        urls[i] = imageURL
    }
    return urls
}

Make sure that your pptURL is file url.
URL(string: "path/to/pdf") and URL(fileURLWithPath: "path/to/pdf") are different things and you must use the last one while initiating your url.

The output should start with "file:///" prefix, f.e.

file:///Users/dev/Library/Developer/CoreSimulator/Devices/4FF18699-D82F-4308-88D6-44E3C11C955A/data/Containers/Bundle/Application/8F230041-AC15-45D9-863F-5778B565B12F/myApp.app/example.pdf