Might have to use some DB queries on the DB for the Moodle to find the file
Query:
select contenhash,component,filearea,filename from `mdl_files` where (`filename` like "%16-01-16.pdf.pdf") ;
*If* the link to the PDF was in an HTML block then component will show htmlblock.
component filearea will show resources.
The contenthash shows the location in /moodledata/filedir/
'spirit of sharing', Ken