Requires OpenOffice 3 for this.
It uses the application drawers to change, so you must select the part of the document that you want to change, if it does not matter if the text or the image. Do not forget to export as PDF.
Keep in mind that the sun pdf import extension enables you to make minor changes, such as editing a title, page number, image size etc. If you want to edit the whole paragraph, you need to create a line by line
There is a more advanced option named PDF Editor but it is not free.