You certainly do NOT want to open PDF with OpenOffice by default. By default you want to open PDF with a PDF viewer.jonhwilliams wrote: Open with > Choose default program... >
With or without the extension, OpenOffice is NOT an editor for PDF. What the extension does is a dirty hack to translate whatever file content originating from whatever program into a vector graphic (a Draw document). In some cases this may help to correct minor errors (e.g. typos) when the original document is not availlable anymore. In other cases it will simply destroy the document or make the program freeze.
PDF is not meant to be an editable document format. PDF is a print-out without paper.