Editores gratuitos de PDF são muito escassos.
O único gratuito que eu conheço é o OpenOffice com Extensão de importação de PDF da Sun .
Do artigo do techsupportalert Um arquivo PDF permite a edição no layout 100% Precisão :
Sun PDF Import ExtensionOpenOffice with Sun PDF Import Extension produces a hybrid PDF / ODF file. The file created will have a normal .pdf file extension. By itself, it is a PDF file and can be viewed by any PDF viewer such as Adobe Reader, PDF-XChange Viewer or Foxit Reader.
On top of this, it contains a source ODF file, which can be opened with OpenOffice directly from the PDF file for editing without loosing any layouts, bookmarks, hyperlinks or formats.
To create a hybrid PDF file, run OpenOffice with Sun PDF Import Extension installed, select "File", choose "Export as PDF", a PDF Options window like the screen shot will open, then tick "Create hybrid file" and click "Export".
This hybrid PDF file saves you in keeping two separate file formats as it has combined two into one. It is ready for sharing and viewing with a PDF reader, yet it can be opened for perfect editing just the way a normal OpenOffice file can be. Probably it will be a good idea to name the hybrid file ending with "-odf.pdf" to differentiate from the normal PDF file.
Sun PDF Import Extension is compatible with OpenOffice.org (3.0 or later) or StarOffice 9.