如何在swift 3.0中将一个pdf文件合并成另一个pdf文件？

import UIKit

func mergePDFs(sourceURLs: [URL], destinationURL: URL) {
    let pdfContext = CGContext(destinationURL as CFURL, mediaBox: nil, nil)
    
    for sourceURL in sourceURLs {
        guard let pdfDocument = CGPDFDocument(sourceURL as CFURL) else { continue }
        
        let pageCount = pdfDocument.numberOfPages
        for pageIndex in 1...pageCount {
            guard let pdfPage = pdfDocument.page(at: pageIndex) else { continue }
            pdfContext?.beginPage(mediaBox: &pdfPage.mediaBox)
            pdfContext?.drawPDFPage(pdfPage)
            pdfContext?.endPage()
        }
    }
    
    pdfContext?.closePDF()
}

let sourceURL1 = URL(fileURLWithPath: "path/to/source1.pdf")
let sourceURL2 = URL(fileURLWithPath: "path/to/source2.pdf")
let destinationURL = URL(fileURLWithPath: "path/to/destination.pdf")

mergePDFs(sourceURLs: [sourceURL1, sourceURL2], destinationURL: destinationURL)