Do you mean PDF reader or a PDF creator program?
Lifehacker reviews some PDF readers - http://lifehacker.com/5328211/five-best-pdf-reader...
If you are interested in creating PDFs, Adobe is the company that developed the PDF file format and the initial creation software, but other applications will allow you to convert the file type the app creates to a PDF. There are also websites that will create PDF versions of other file types.
Hope this helps!