Reason:

Missing SaveURLPrefix or missing metadata in source images

Solution:

In order to have FSI Pages offer PDF files for download, you will need to convert the PDF file in FSI Pages Converter with the “Enable PDF output” option enabled. This will ensure the proper information regarding the filename is written in the IPTC metadata of the images.

Also the SaveURLPrefix Parameter must be set with the full path to the PDF file (but without the PDF filename).
E.g. “http://www.example.com/pdfs/”