Export to PDF that has Arabic character

when I export the model that has Arabic character to PDF the character doesn't display correctly. I tried to use the streamWriter to change the encoding but it doesn't work because the export method takes only stream this is my code

using (Stream fileStream =File.Create(filePath)){
var exporter = new PdfExporter() { Width = 600, Height = 400};
exporter.Export(plotView.Model,fileStream);
fileStream.Close();
}
Note: I am using oxyplot in xamarin-android
thank you