Edit my signature in PDF file in my iPad application

Question

In my iPad application I want to add signature in my pdf file.

I already do perform following steps:

1. Open pdf in UIView (zooming is not implemented yet).
2. Add one transparent subview (UIImageView) and draw signature on that.
3. Save all screen using UIGraphicsGetImageFromCurrentImageContext() as a image.
4. Convert and save the image as a pdf.

This is works fine but pdf quality is very poor.

But now I want to add a signature/image as a pdf metadata. Same as a markup and commenting features of PDF.

Is there any help or sample code is available for the same?