One question before purchase

just render to bitmap object?
see Page.renderToBmp
or PDFSimple class in demo project?

To resume:
- actually it's not possible to modify pdf structure adding pages, text or other objects that aren't supported annotations
- you can produce both bmp and dib images from actual pdf page and store them to filesystem, db or programmatically alter it
- you shall retrieve page movement, zoom, coordinates and use that information to add OS objects upon them with a custom UI