The most common application is the Internet Security Certificate. These files are provided by various providers, also called certificate authority, such as Thwate or VeriSign. These will then be installed on the web server to ensure the validity of the website being accessed.
Mostly used in conjunction with an encrypted, secure HTTPS connection, the CER files can be viewed in any browser. Depending on the browser, a simple or double-click on the lock symbol is sufficient.
Most often resolving problems with opening CER files is very simple. Just install an appropriate program that supports such files. All of the listed programs support CER files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of CER files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate CER files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Safari applications is not on the list, select "Browse" option in order to manually locate the directory where Safari has been installed.
Sometimes problems with opening CER files may not lie with the application itself, but can arise due to other causes, such as: