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
Best Answer
To open the file, use any PDF reader. I tested this by opening a self-signed pdf file in linux using epdfviewer. Even though the .pfx file was not in the system, the viewer did not complain, or even asked for the .pfx file.
I believe that the .pfx file is only needed for signing the document, not for opening it. In this way, it acts as a private key file.
Update: The updated question clarifies the requirements. You're looking for a PDF viewer that shows the signature field and also allows you to sign the document in the signature field. epdfviewer does not do that.
As I mentioned in the comments, CabaretStage does show the signature field and allows you to place the signature on that field as well. The free version adds a watermark, so you need to purchase it.
Apparently, Foxit Reader also works, but I was not able to get it to work on my system, so I cannot confirm it.