Sun has released an OpenOffice extension that allows you to import a PDF and allow basic editing. It uses Draw and Impress, as opposed to the more obvious Writer, to preserve the layout of the document. Forms are not yet supported. In future versions the developers aim to support more editing capabilities, and less on layout, by using… Writer.
There are versions available for Windows, Linux (32 and 64 bit), MacOS X and Solaris (x86 and Sparc). According to the comments in the Extension, it is kind of hit or miss if the extension works for your installation, but that explains why Sun is still calling it Beta.