KSI Explorer is a program created to open and manage documents that have an electronic signature, which is becoming more common each day because it's a system to be able to send notifications a much quicker and more securely than handing them in by hand.
Sign your documents electronically
The program is compatible with the vast majority of modern standards, like CMS/PKCS#7 (Attached and Detached) and TS 101 733 (CAdES) X-L or TS 101 903 (XAdES). Furthermore, it's capable of using several card readers to open or sign the documents, like that of an electronic ID, for example.
A decent tool to work with documents that have been signed electronically.
The program's interface is similar to that of a common file explorer, so that, even if you aren't used to working with files that include an electronic signature, you shouldn't have any problem to be able to adapt to using the application. Moreover, it has various skins, thanks to which you will be able to customize the development's aspect.