We have some PDF files which are secured by a .pfx certificate. On Windows we can use Adobe Reader to read these PDF files (with previously imported certificate).
I've googled for a long time but I can't find a PDF reader which can open this.
NOTE: Just so it's clear. If I were to open a PDF file that had this digital signature applied to it, and it was opened in say, Evince it would display like this:

While Acrobat Reader (acroread) like this:


PDF File for the above is here: http://adobetrainer.co.uk/Resources/sign-a-pdf-with-reader-enabled.pdf
openssl pkcs12to decrypt it (provided you have the appropriate key) - see thepkcs12man page.