It completely depends on the nature of the original PDF. For example, when you say you want to copy&paste an article, well, what is the article? Is it really text? And you want it to remain editable text? Then don't use Photoshop, because it rasterizes everything.
I would suggest you start with Acrobat 6.0 Professional. It has text and graphic selection tools, and allows you to extract such pieces to other programs.
You can only paste into the PDF images that replace current images. In other words, you can't use Acrobat to "place" new images or dramatically alter the document layout, like you can with a Page Layout program.
But just to reiterate, if the PDF contains actual text (not a scan or a "picture" of text"), and some graphic images, and your goal is to extract those to other programs where they go off and live happy lives outside of the PDF, then Acrobat 6.0 Professional should do the job.
Thomas D. Greer
Providing PostScript & PDF
Training, Development & Consulting