NSData - Write to temporary file / directory

I am a little lost on my quest to -

1. Download a CKAsset (PDF File)
2. Assign a Temporary Filename
3. Write the contents of the CKAsset to the filename

I have managed to download the CKAsset and display the contents in a UIWebView, however I am stumbling over steps 2 and 3, I have a filename from a String, and despite trying a variety of WriteToFile combinations I receive errors.

My code is thus :

let filename = record.object(forKey: "materialsFilename")

                        if  materialsType == "PDF" || materialsType == "pdf" {


                            if let asset1 = record.object(forKey: "materialsFile") as? CKAsset {
                                let doc1Data : NSData? = NSData(contentsOf:asset1.fileURL)

                                let path = NSURL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(filename as! String)


                                let contentsOfFile = doc1Data
                                var error: NSError?

                                // Write File
                                if contentsOfFile.writeToFile(path, atomically: true, encoding: String.Encoding.utf8, error: &error) == false {
                                    if let errorMessage = error {
                                        print("Failed to create file")
                                        print("\(errorMessage)")
                                    }
                                } else {
                                    print("File \(filename) created at tmp directory")
                                }

This version presents the error -

Cannot invoke 'writeToFile' with an argument list of type '(URL?, atomically: Bool, encoding: String.Encoding, error: inout NSError?)'

The temporary file once created will be passed to a UIActivityViewController, to print / email / airdrop the PDF, having only a CKAsset name, the the UIActivityViewController cannot associate the file type to any of the users installed apps, save for print.

After a little head scratching and reviewing my choices following the pointers above, I changed tack and didn't really need to write to a file, just rename the CKAsset, which I achieved with the following script -

let materialsType = record.object(forKey: "materialsType") as! String

                        let filename = record.object(forKey: "materialsFilename") as! String

                        if  materialsType == "PDF" || materialsType == "pdf" {

                            if let asset1 = record.object(forKey: "materialsFile") as? CKAsset {

                                let doc1Data : Data? = Data(contentsOf:asset1.fileURL) as Data?
                                let fileURL = NSURL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(filename)
                                self.materialsWebView.load(doc1Data! as Data, mimeType: "application/pdf", textEncodingName: "UTF-8", baseURL: NSURL() as URL)
                                self.filenameURL = [(fileURL)]
                            }

The key seemed to hinge on two lines -

let fileURL = NSURL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(filename)

and

self.filenameURL = [(fileURL)]

Which generates the filename for the UIActivityViewController and thus opens up the access to a number of additional Apps.