PDF Page Merging and editing

I'm in need of someone who can merge and edit PDF pages. Specifically, I need to add pages from existing PDFs, which I have ready. As for design elements, I'm not sure yet if I will need any, but I'm open to the possibility. Therefore, I would request that the freelancer be able to add design elements to the PDFs if the need arises. If this is something that you can do, I'd love to hear from you.
Code for merging must be executable on .Net 4.x website. 3rd party controls will be considered.
Specifically be able to merge 3 small pdf files into 1 pdf page. More details can be provided