In the post processor text field you can use the $EXECUTABLE variable to reference the executable that is currently being post-processed. The working directory of the executed process is the directory your config is located in so you can use relative file names for key or certificate files. If the signing command cannot replace the executable directly, but rather needs a separate output file, use the $OUTFILE variable. It will receive a temporary output file name that will be moved back to the processed executable by install4j after the post processor has completed.