The pdf file type is mainly associated with Acrobat, Adobe Systems Incorporated, Adobe PDF Reader, Brava! Reader Free PDF Viewer, Zoho Viewer (Web Viewer), PDF-XChange Viewer, and with the following MIME types: application/pdf, application/x-pdf, application/acrobat, applications/vnd.pdf, text/pdf, text/x-pdf

This SonicWALL signature identifies HTTP downloads of Content-Type: application/x-pdf.