The Mac's operating system (OS X), has always been very PDF-aware. PDF documents can be opened by the built-in 'Preview' software, and you can also create PDFs very easily by 'printing' the document, then choosing 'Save to PDF' from the little menu at the bottom left of the print dialogue box. 

The most common PDF-related task, apart from those mentioned above, are to join a number of PDFs into a single one, and to split a PDF into a number of separate ones (splitting into individual pages is usually sufficient since they can then be joined again into the required parts). The two latest versions of the Mac OS X (10.5 and 10.6) have  the necessary tools and others built into the Preview utility. See How to merge pdf files with preview in Leopard to find out more. The Adobe Acrobat suite  is another well known tool for the job, but it is very expensive and overkill for most people's needs.

So, if you have a Mac with OS X 10.3 or 10.4 and want to do basic PDF editing, you will need software from a third party. Here is a list of several such packages.