First of all: "properly convert PDF to DOC/ODF and back to PDF" - Convertion is nearly always a loss operation. No tool can offer you a 100% correct conversion forth and back.
As far as I know, there is no converter or else that offers a PDF to WDF (WhateverDocumentFormat) conversion, since it is basically not possible.
For the PDF Editor, I use and recommend "Master PDF Editor". It is available in the ubuntu repositories or from their website: http://code-industry.net/pdfeditor.php
For ODT/DOC to PDF operations Libre-/OpenOffice is simply unbeaten.