Viewing visual Signature in iOS-App

Question

I'm using the UIDocumentInteractioncontroller for displaying pdfs and images in my application. If i try to display a pdf with a visual signature, the signature is not shown.

On the other hand, if I use the native mail app to preview the same pdf, the visual signature is shown.

Am I missing some configuration or is the native app using a different DocumentController?

Here's my code:

UIDocumentInteractionController *documentInteractionController =[UIDocumentInteractionController interactionControllerWithURL:[NSURL fileURLWithPath:navigatorImpl.fileUrl]];
    documentInteractionController.delegate = self;
    [documentInteractionController presentPreviewAnimated:YES];

Thanks in advance!

Herbert