Recently, I installed a new version of FreePDF (also known as FreePDF XP, its earlier name). Unfortunately, the latest version does not include the PDF toolkit (pdftk) any more (which is necessary for giving a watermark to the PDF-file – e.g. a letterhead paper), so it had to be installed manually and the pdftk.exe and the library libiconv2.dll had to be moved to the FreePDF main directory.
Unfortunately, after doing this, I encountered the error 5, whenever I tried to use the profile with the watermark. After some checking, it turned out that FreePDF needs a special version of the PDF toolkit. As it may change with the FreePDF versions, I am not giving a special version here, just try some older versions of the PDF toolkit, if you have the same experience.
Find information in English on the 2-click solution here: http://yro.slashdot.org/story/11/09/03/0115241/heises-two-clicks-for-more-privacy-vs-facebook