For those who always want to modify pdf; may be this can help;
download and install the wonderful pdftohtml from http://sourceforge.net/projects/pdftohtml (developed by Gueorgui Ovtcharov and Rainer Dorsch,
maintained by Mikhail Kruk).

To use this service menu;
1. right -click to convert pdf to html.
2. edit your html using text editor, openoffice or ....
3. you can then convert back to pdf.

Note:
1. not all pdf will output to text.
2. problem with 'lanscape' text, or landscape layout.
3. some of the pdf convert from openoffice is compressed, you may not get proper text from pdftohtml.
4. you may need pdftk to uncompress pdf file.
5. Not working for Chinese/Japanese, may someone comment on this.

Hope this is useful
tanm