PDF Converter

I recently purchased the PDF Converter app through the apple store, this one:

Whenever I try to use it whether it is to compress a pdf or convert (or whatever) and I select the place for the compressed or converted file to be downloaded to (whether in downloads, desktop or wherever). I press download and nothing happens - nothing is downloaded? Where is my document going?

Maybe I am doing something wrong?

Any advice greatly received.

Thank you