Are you sure thay you want to edit PDF content directly? You can definitely accomplish this with ElementReader/Writer (ala ElementEdit sample), but working with image annotations may be simpler. This way you can also take advantage of provided annotation tools and source code to select, move, scale, delete annotations etc.
To make this happen you could create a custom annotation and generate its apperance (e.g. see https://groups.google.com/d/msg/pdfnet-sdk/q51fmeKjmWw/HyRpQ9jEpYwJ also search for SetAppearance() - for more samples https://groups.google.com/forum/?hl=en&fromgroups#!searchin/pdfnet-sdk/SetAppearance), you would then modify tools source code (which is priovided to all licensees) to diplay your image during interactive editing.
Hope this makes sense.