This article shows how to add an image to a pdf (annotation and content):

You can create an instance of PDFDocImage in this way:

NSString *path = @"path_to_image";
PDFDocImage *i = [m_doc newImageJPEG:path];

or create a PDFDocImage from CGImageRef
// Get PDFDocImage instance from CGImageRef (keeping alpha channel)

PDFDocImage *i = [m_doc newImage:ref :YES];
// Add the image

[page addAnnotBitmap:i :&rect];