How to save loaded PDF document in application level?

namespace SavePDFUsingNative
{
    public interface ISave
    {
        string Save(MemoryStream fileStream);
    }
}

public MainPage()
{
     InitializeComponent();
     m_pdfDocumentStream =        typeof(App).GetTypeInfo().Assembly.GetManifestResourceStream("SavePDFUsingNative.Assets.GIS Succinctly.pdf");
     pdfViewerControl.LoadDocument(m_pdfDocumentStream);
     pdfViewerControl.DocumentSaveInitiated +=         PdfViewerControl_DocumentSaveInitiated;
}
 
private void PdfViewerControl_DocumentSaveInitiated(object sender, Syncfusion.SfPdfViewer.XForms.DocumentSaveInitiatedEventArgs args)
        {
            string filePath = DependencyService.Get<ISave>().Save(args.SaveStream as MemoryStream);
            string message = "The PDF has been saved to " + filePath;
            DependencyService.Get<IAlertView>().Show(message);
        }
 

[assembly:Dependency(typeof(SavePDFUsingNative.Droid.SaveAndroid))]
 
namespace SavePDFUsingNative.Droid
{
    public class SaveAndroid : ISave
    {
        public string Save(MemoryStream stream)
        {
            string root = null;
            string fileName = "SavedDocument.pdf";
            if (Android.OS.Environment.IsExternalStorageEmulated)
            {
                root = Android.OS.Environment.ExternalStorageDirectory.ToString();
            }
            Java.IO.File myDir = new Java.IO.File(root + "/Syncfusion");
            myDir.Mkdir();
            Java.IO.File file = new Java.IO.File(myDir, fileName);
            string filePath = file.Path;
            if (file.Exists()) file.Delete();
            Java.IO.FileOutputStream outs = new Java.IO.FileOutputStream(file);
            outs.Write(stream.ToArray());
            var ab = file.Path;
            outs.Flush();
            outs.Close();
            return filePath;
        }
    }
}

[assembly: Dependency(typeof(SavePDFUsingNative.iOS.SaveiOS))]
 
namespace SavePDFUsingNative.iOS
{
    public class SaveiOS : ISave
    {
        public string Save(MemoryStream fileStream)
        {
            string path = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
            string filepath = Path.Combine(path, "SavedDocument.pdf");
 
            FileStream outputFileStream = File.Open(filepath, FileMode.Create);
            fileStream.Position = 0;
            fileStream.CopyTo(outputFileStream);
            outputFileStream.Close();
            return filepath;
        }
    }
}

[assembly: Dependency(typeof(SavePDFUsingNative.UWP.SaveWindows))]
namespace SavePDFUsingNative.UWP
{
    public class SaveWindows : ISave
    {
        MemoryStream stream;
        StorageFolder folder;
        StorageFile file;
        public string Save(MemoryStream documentStream)
        {
            documentStream.Position = 0;
            stream = documentStream;
            SaveAsync();
            return Path.Combine(ApplicationData.Current.LocalFolder.Path, "SavedDocument.pdf");
        }
 
        private async void SaveAsync()
        {
            folder = ApplicationData.Current.LocalFolder;
            file = await folder.CreateFileAsync("SavedDocument.pdf", CreationCollisionOption.ReplaceExisting);
            if (file != null)
            {
                Windows.Storage.Streams.IRandomAccessStream fileStream = await file.OpenAsync(FileAccessMode.ReadWrite);
                Stream st = fileStream.AsStreamForWrite();
                st.SetLength(0);
                st.Write((stream as MemoryStream).ToArray(), 0, (int)stream.Length);
                st.Flush();
                st.Dispose();
                fileStream.Dispose();
            }
        }
    }
}