what is the difference between Adobe Reader and Digital Editions?

I can not understand why I should download so many different programs. I have hard disc space issues.

I have a Samsung Notebook 905S and I do want to "clean" the programs.

Who can help me to tell me what are the best programs of Adobe? Could I implement with Adobe Digital Edition the PDF files f.e. also from those pages? http://tourism-competences.com/ or http://wips.ch/ or from that one: Executive Limousines Services Switzerland | SUV VAN Sedan