Placing the following snippet in an .htaccess file in a directory will force all pdfs (.PDF and .pdf) there to be downloaded to the computer rather than opened in the browser. This is good for occasions when IE is caching the PDF and users aren’t seeing the latest version.

<FilesMatch "\.(?i:pdf)$">
  ForceType application/octet-stream
  Header set Content-Disposition attachment
</FilesMatch>