Acrobat IS PDF, but it really depends on what you need.
As stated above, you can print anything to PDF. That might not be the most optimum compression and all, but it is convenient and free.
Most, if not all, scanners come with software that will scan directly to PDF, generally doing OCR to make the text searchable.
Preview can do some PDF manipulation (annotations, combine and remove pages, etc), but If you need the more advanced features of Acrobat, that's likely the best choice. There are some other programs that provide those advanced features, but I've never used them.