desktop file exec working firectory

[Dj YB]

Hello,
I am creating a desktop file for a service menu, and can't find out how to use 
the directory from which the action was launched.

this is how it looks:

Exec=convert %F `kdialog --title "save PDF" --getsavefilename join.pdf`;

this is how I want it to look:

Exec=convert %F `kdialog --title "save PDF" --getsavefilename $PWD/join.pdf`;

that doesn't work.

thanks in advance,
YB.