WebPlus X5: pdfindex.html

The owner of a Webplus X5 site that I designed has said that according to Google Analytics the page with the fourth largest number of hits is /pdfindex.html

This page does not physically exist on the site. Does anyone know what it is? Has it been generated automatically? They do upload PDF files to the site with links from WP pages.

Thanks and a happy New Year,
Gillian