Substitute web property onto filename

Hi All, 

I currently have a web service that a user would input a students name and other details that would be collated into a PDF file that is then emailed to myself. What I would like is to be able to save that PDF file with the @student parameter as the filename. I have tried to concatenate "@student" but feel like the file writers take the destination input literally? 


Any help would be greatly appreciated

Jack