Once in a blue moon you might just want to edit a PDF and not have access to the original document it was created from. Obviously if you need to do this a lot then purchasing the full version of Adobe acrobat is the best solution but free and low cost solutions do exist.
One of these is Sun’s PDF import plugin for OpenOffice. Originally native import of PDF’s was intended to be a standard feature in this free office suite but development did not keep pace with the release timetable. It’s still in beta but can be a useful solution with the right PDF file. For free it’s certainly worth trying.
Open Office is available for Windows, Mac and Linux.
Windows users may also care to consider downloading a trial of the commercial NitroPDF program.