我可以使用哪种图形格式的图层？

I need to be able to take multiple images and save them to a file that can then be read by a graphics program like Photoshop or Illustrator and edited. I need to be able to do this in a C#/.Net environment. It looks like PDF's have the capabilities to do layers but I am not sure if any of the free components like PDFSharp will support the layers. It would be nice to be able to write directly to a Photoshop file (PSD) but I haven't found anything that can do that. Any other suggestions? Thanks.I need to be able to take multiple images and s