Rename the download pdf file using swift iOS

I am successfully downloading a PDF from api end point. Once pdf is downloaded, the title of pdf is : PDF document.pdf . How to change the title of PDF?

I tried to update metadata of PDF using PDFDocumentAttribute (see below), but it is not working.

var metadata = pdfDocument.documentAttributes!
metadata[PDFDocumentAttribute.subjectAttribute] = "subject attribute"
metadata[PDFDocumentAttribute. titleAttribute] = "title attribute"
pdfDocument.documentAttributes = metadata

Note: I am not using FileManager

How I am fetching PDF:-

let task = session.dataTask(with: urlRequest) { (data, _, error) in
            DispatchQueue.main.async {
                guard let unwrappedData = data, error == nil else {
                    completion(.failure(error ?? Constants.dummyError))
                    return
                }

                guard let pdfDocument = PDFDocument(data: unwrappedData) else {
                    completion(.failure(error ?? Constants.dummyError))
                    return
                }

                completion(.success(pdfDocument))
            }
        }

try this:

pdfDocument.documentAttributes?["Title"] = "my title attribute"

or

pdfDocument.documentAttributes?[PDFDocumentAttribute.titleAttribute] = "my title attribute"

Similarly for PDFDocumentAttribute.subjectAttribute.

The above will set the Title of your document, and when you save it, the file name will be whatever file name you give it.

EDIT-1: saving the pdfDocument to a file with a chosen file name.

       DispatchQueue.main.async {
            guard let unwrappedData = data, error == nil else {
                completion(.failure(error ?? Constants.dummyError))
                return
            }
            guard let pdfDocument = PDFDocument(data: unwrappedData) else {
                completion(.failure(error ?? Constants.dummyError))
                return
            }
            
            // set the Title
            pdfDocument.documentAttributes?[PDFDocumentAttribute.titleAttribute] = "my title attribute"
            
            do {
                // save the document to the given file name ("mydoc.pdf")
                let docURL = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false).appendingPathComponent("mydoc.pdf")  // <-- here file name
                pdfDocument.write(to: docURL)
                print("\n docUrl: \(docURL.absoluteString)\n")
            }
            catch {
                print("Error \(error)")
            }
            completion(.success(pdfDocument))
        }